Ce Phy Mock Paper B1 Q&a

HKCEE Mock Examination Physics Paper 1

Name: ____________________

Class No.: _________________

3 (Time allowed: 1 4 hours) This paper must be answered in English. 1.

Write your name and class number in the spaces provided on this cover.

2.

This paper consists of TWO sections, Section A and Section B. Section A carries 60 marks and Section B carries 40 marks.

3.

Answer ALL questions in each section. Write your answers in the spaces provided.

4.

5.

Some questions contain parts marked with an asterisk (*). In answering these parts, candidates are required to give paragraph-length answers. In each of these parts, one mark is allocated to assess candidates’ ability in effective communication. Take g = 10 ms-2.

6.

Unless otherwise specified, numerical answers should be either exact or correct to 3 significant figures. Useful Formulae in Physics

(a) Relationships between initial velocity u, uniform acceleration a, final velocity v and displacement travelled s after time t: v = u + at

1 s = ut + at 2 2

v 2 = u 2 + 2as

(b) Potential energy gained by a body of mass m when raised through a height h is mgh. 1 2 (c) Kinetic energy of a body of mass m moving with speed v is 2 mv . 1

(d) Power = force x velocity (e) Equivalent resistance of two resistors R1 and R2 (1) in series = R1 + R2 R 1R 2 (2) in parallel = R + R 1

(f)

2

Power = potential difference x current

2

Section A (60 marks) Answer ALL questions in this section and write your answers in the spaces provided.

1.

Question No.

1

2

3

4

5

6

7

8

9

Marks

7

7

6

6

9

5

8

6

6

In a ski jumping event, athletes must ski down a steep ramp of 120 m tall and 'fly' in air. The winner must be able to jump over a long distance.

Figure 1 An athlete accelerates from rest at g sin θ, where g is 10 m s−2 and θ is the angle between the ramp and the horizontal, down the straight portion of the ramp and it takes him 6 s before he enters the curved ramp. (a) Find the length of the straight portion of the ramp. (4 marks) ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ (b) Hence, find the speed of the athlete before he skis on the curved ramp. (3 marks) ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________

3

2.

Read the following passage about hang time and answer the questions that follow:

In a basketball game, it is not unusual to see that players shoot the ball while they hang in air. If we compare the hang-time, which is the period of time staying in air without touching the ground, of different players, we might find that the hang-time of Michael Jordan is relatively long. What is his secret to do so? As we know that when we jump up, our motion is governed by the gravity of the Earth. How long that we can hang in air depends entirely on the acceleration due to the gravity and our speed leaving the ground, and the speed that we leave the ground in turn depends on the size of the force that we push ourselves against the ground. Hence, Jordan's long hang-time could be because of his high jumping speed. In addition, since Jordan tends to pull his legs up in the mid-air as he jumps and he holds onto the ball longer than other players, i.e. he shoots the ball until he starts to fall down, his hangtime would appear to be longer than other players. Reference: http://www.exploratorium.edu/sports/sports_faq.html (a)

According to the article, how can Michael Jordan manage to have long hang-time? (3 marks) ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ (b)

In a standard basketball court, the basket is 10 feet above the ground. If a player jumps 3 feet before shooting, calculate the time period for the player to complete the whole shooting motion. (Given: 3 feet = 0.914 m) (4 marks) ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________

4

3

Fountain 27 Fever sport boat has a mass of 2338 kg. The power of its engine is 425 horsepower and it can travel at a speed up to 31.3 m s−1. (Given: 1 horsepower = 746 W)

Figure 3 (a) Find the shortest time that the boat can attain the speed of 31.3 m s−1 from rest.(3 marks) ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ When the boat travels at a constant speed of 31.3 m s−1, what is the friction acting on the boat? (3 marks) ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ (b)

4

The depth of the sea affects the wavelength of the water waves on the sea. Consider the following case. The wavelength reduces from 3 m to 2 m when the wave travels from region A to region B. 3m

2m

Region A

Region B

Figure 4 (a) Name this wave phenomenon. Which region is shallower, A or B? (2 marks) ________________________________________________________________________________ ________________________________________________________________________________

5

4. (b) In which region does the wave travel faster? (1 mark) ________________________________________________________________________________ If the wave speed in the faster region is found to be 1.5 m s–1, find the wave speed in the slower region. (3 marks) ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ (c)

5

An object is placed in front of lens L. The following ray diagram shows that a light ray from the object is refracted by L.

Figure 5 (a) What type of lens is L? (1 mark) ________________________________________________________________________________ (b)

By adding suitable light rays to Figure 5, find the image distance, magnification of the image, and the focal length of the lens. (5 marks) ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ (c) If the lens is moved 30cm to the right while the object is kept at the same position, find (1) the image distance, and (2) the magnification. (3 marks) ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________

6

6

Rheostat is a common electrical component in physics laboartories. The following diagram shows a '15 Ω, 8 A' rheostat connected by wires. B

15 Ω 8 A max

X

A Y

Figure 6 (a) Explain the meaning of '15 Ω' on the label. (1 mark) ________________________________________________________________________________ (b) To obtain the maximum equivalent resistance across X and Y, where should the sliding contact of the rheostat be? Hence, calculate the maximum equivalent resistance across X and Y. (4 marks) ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ 7

In Figure 7, a coil is put between the poles of a magnet. spring

current I P I

N

N

S

A

B

D

C

S

I I

Q

axis

Figure 7 (a)

Mark on the Figure 7 the directions of the forces acting on the sides AD and BC at the moment shown. Hence, find out the direction in which the coil turns as viewed from P. (3 marks) ________________________________________________________________________________ ________________________________________________________________________________

7

7.

(b)

Is there any force acting on the sides AB and CD when the coil starts to turn? Do these forces affect the rotation of the coil? (3 marks) ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ (c)

The springs at the top and at the bottom of the coil provide a force to stop the coil from turning. (i) The larger the angle that the coil turns, the larger is the size of a physical quantity. What is this physical quantity. (1 mark) ________________________________________________________________________________ (ii) Hence, suggest an application of this set-up. (1 mark) ________________________________________________________________________________ 8

An α source is placed at a distance d from a G-M tube which is connected to a scaler. At a certain moment, the count is shown below. scaler

d

2271

source G-M tube

Figure 8 (a) What happens to the reading on the scaler when distance d is increased? (2 marks) ________________________________________________________________________________ ________________________________________________________________________________ *(b)

If distance d is too large, the G-M tube cannot detect the radiation from the source. A student explains this by saying that the radiation falls to the ground due to gravity. Suggest how to show that the student is wrong using the above apparatus. (4 marks) ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________

8

9

Biological effects of radiation on human body is measured in sieverts (Sv). It is found that our body will receive 4 × 10−6 mSv if we take in a bowl of rice.

Figure 9 (a)

Why are the biological effects NOT measured in number of counts of the radiation? (3 marks) ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ (b)

Mary eats 3 bowls of rice every day and she worries about whether she has absorbed too much radiation due to this kind of food. As a Physics student, what comment would you give her? Explain briefly. (Given: annual dose of radiation from natural background is about 2 mSv) (3 marks) ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________

9

Section B (40 marks) Answer ALL questions in this section and write your answers in the spaces provided. Question No.

10

11

12

13

Marks

10

9

11

10

10. This question is about the wave phenomena of sound. (a) A boy is shouting in front of a door. This produces a series of sound waves approaching the doorway. The top view is shown in Figure 10a. sound waves

doorway

doorway

Figure 10a (i)

Sketch the wave pattern formed on the other side of the doorway. (2 marks) (ii) Name this wave phenomenon. (1 mark) (iii) Explain how the behaviour of a beam of light waves passing through a doorway is different to that of sound waves. (2 marks) (b)

Two identical loudspeakers P and Q emit sound of the same frequency and intensity as shown in Figure 10b. X

P

CRO

C

R signal generator

microphone Q

Figure 10b

Y

Point C is equidistant from the loudspeakers and line XY is parallel to the line joining the loudspeakers. A microphone connected to a CRO is moved along XY to detect the sound. The variation of the amplitude of the CRO trace with the position of the microphone is shown in Figure 10c. amplitude of CRO trace

X

C

Y 10

position of microphone

Figure 10c (i) (ii)

Explain why the amplitude shows alternate maxima and minima. Explain why the amplitude at the minimum points is non-zero. marks)

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(2 marks) (3

________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________

12

11

B Two charged spheres A and B are suspended by two identical nylon threads. They remain at rest as shown in Figure 11 A

Figure 11 (a) *(b)

Draw a labelled diagram to show all the forces acting on A.

(3 marks)

Two students make the following remarks: Mary: Both spheres carry positive charges. Peter: The force acting on B by A is larger than the force acting on A by B. Explain whether each of the above remarks is correct. (5 marks)

(c) Explain why A is at rest at a lower height. (1 mark) ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________

13

12

A student wants to test three transformers, X, Y and Z. He uses a variable voltage supply to vary the primary voltage and a voltmeter to measure the secondary voltage. The results are as follows: primary voltage / V 4

X

Y

3 Z

2 1

0

1

2

3

4

secondary voltage / V

Figure 12 (a)

Should the student use a d.c. voltmeter or an a.c. voltmeter? Explain briefly. marks)

(2

(b)

Which is a step-up transformer?

(c)

The student wants to connect an iron marked ‘110 V, 1100 W’ to the mains of 220 V. (i) Which transformer should the student use? (1 mark) (ii) Calculate the cost to switch on the iron for 2 hours if it operates at proper rate. (Given: One kilowatt-hour of electrical energy costs $0.9.) (2 marks) (iii) If the efficiency of the transformer in (i) is 80%, what is the primary current of the transformer? (2 marks)

*(d)

In order to reduce the power dissipated in the transmission lines, high voltage transmission is used. Explain why high voltage transmission can reduce the power loss. (3 marks)

(1 mark)

________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________

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________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________

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13. A student wants to measure the melting point of a substance. He fills half of a boiling tube with that substance and heats it. After the substance melts completely, he lets the substance cool down and records the temperature every minute. The following results are obtained. Time / min Temperature / °C

0 80

1 70

2 60

3 58

4 58

5 58

6 56

7 49

8 42

9 38

10 32

(a) Using a scale of 1 cm to 10 °C and 1 cm to 1 minute, plot a graph of temperature against time, ranging from 0 to 80 °C. (4 marks) (b) (i) Find the melting point of the substance from the graph. (1 mark) (ii) At which time interval does the substance have both liquid and solid states?(1 mark) (c) (i)

If the substance lost 30 W at its melting point, how much energy is lost to the surroundings? (2 marks) (ii) If the mass of the substance used is 0.05 kg, what is the specific latent heat of fusion of the substance? (2 marks)

________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________

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________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ END OF PAPER

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Paper 1 Solution Physics Paper I Section A 1. (a)

Let d be the distance of the straight portion of the ramp. 1 By s = ut + 2 at2,

1M

1 × (g sin θ) × 62 2 1  120   × 36 d = × 10 ×  2  d  d = 147 m By v = u + at,

1A

d=0+

(b)

1A 1A 1M

v = 0 + (g sin θ) × 6  120  = 10 ×  147  × 6  

1A 1A

= 49.0 m s−1

2.

(a)

(b)

Jordan has long hang-time because he jumps at a high speed,

1A

he tends to pull his legs up when he jumps, and

1A

he holds onto the ball longer than other players. Let t be the time that the player rises to the highest point.

1A

Take upwards as positive. u = v − at ....................................................................(1)

2M

1 s = ut - 2 at2................................................................(2) (1) --> (2):

1 s = (v − at) × t - 2 at2

0.914 = [0 −(−10t)) × t − 5t2 t = 0.428 s

1A

The time period for the whole motion = 2t = 0.856 s

3.

(a)

1A

When all the energy provided by the engine is converted to the kinetic energy of the boat, the time required to attain the speed is the shortest. By E = Pt, 1M

mv 2 P 2 1 2 × 2338 × 31.3 = 425 × 746

t=

1 2

1A

= 3.61 s The shortest time that the boat can attain the speed of 31.3 m s−1 is 3.61 s.

18

1A

(b)

Let f be the friction acting on the boat. By P = Fv,

1M

425 × 746 = f × 31.3

1A

f = 10 129 N

1A

The friction acting on the boat when it travels at a constant speed of 31.3 m s−1 is 10 129 N.

4.

(a) Refraction

1A

Region B is shallower. (b) The wave travels faster in region A. (c) vA : vB = λ A : λ B

1A 1A 1M

1.5 : vB = 3 : 2

1A

–1

vB = 1 m s

5.

(a) (b)

1A

Convex lens.

1A

Correct rays Correct image( REAL image ) From the ray diagram,

1A 1A

image distance = 60 cm

1A 1A

image distance 60 cm = magnification of the image = =2 object distance 30 cm focal length = 20 cm (c) (i) image distance = 30 cm

6.

(a) (b)

1A 2A

image distance 30 cm = (ii) magnification of the image = = 1/2 object distance 60 cm

1A

It is the maximum resistance that can be provided by the rheostat. The sliding contact should be in the middle of A and B.

1A 1A

At this position, the circuit is equivalent to the following combination: 7.5 Ω X

A

B

Y

7.5 Ω

The equivalent resistance across X and Y = (7.5−1 + 7.5−1)−1 = 3.75 Ω The maximum equivalent resistance across X and Y is 3.75 Ω.

19

2M 1A

7.

(a) I P

I

A

B

F F

N D

C

S

I

Q I

(Force acting on side AD points into the paper.)

1A

(Force acting on side BC points out of the paper.) The coil turns in clockwise direction as viewed from P.

1A 1A

When the coil starts to turn, an upward force acts on the side AB and

1A

a downward force acts on the side CD.

1A

These forces do not affect the rotation of the coil.

1A

(i) Current (flowing in the coil). (ii) This set-up can be used to measure the current flowing in the coil/ammeter.

1A 1A

(a)

The count rate should decrease until it drops to the background level.

2A

(b)

Turn the G-M tube upright so that its opening faces upwards. Hang the source above and facing the G-M tube. Slowly increase the distance d. The count rate should decrease until it drops to the background level. This shows that the student is wrong. (For effective communication)

1A

(b)

(c)

8.

9.

(a)

(b)

Biological effect depends on type of radiation ( effective level ) parts of the human body radiated ( equivalent level ), the number of counts cannot show the actual biological effects on human body. Annual dose due to taking in rice = 4 × 10−6 × 3 × 365 = 0.00438 mSv << 2 mSv Since this figure is much smaller than the annual dose from natural background (~0.2%), I will tell her not to worry about her eating habit.

20

1A 1A 1C

1A 1A 1A

1M 1A 1A

10.

(a)

(i)

2A

(1A for the shape) (1A for wavelength remains unchanged) (ii)

Diffraction.

1A

(iii)

The beam of light passes straight through the doorway without spreading.

1A

It is because the size of the gap is too large when compared

1A

with the wavelength of light. (b)

(i)

The amplitude reaches a maximum where sound waves from

1A

P and Q reinforce each other (constructive interference), and a minimum where they cancel each other

1A

(destructive interference). (ii)

The intensity of sound waves decreases with distance,

1A

so the intensities of sound waves from P and Q are not

1A

equal. Sound waves from P and Q cannot cancel each other

1A

completely at the points of destructive interference.

11.

tension

(a)

A

electrostatic force by B

weight

(1 mark for each correct force with correct FULL name) (b)

3 × 1A

Mary is incorrect.

1A

Since A and B repel each other, they carry the same charge, which can

1A

be positive or negative. 1A Peter is incorrect. The force acting on B by A and the force acting on A by B form an

1A

action-and-reaction pair. They are equal in magnitude but opposite in direction. (For effective communication.)

1C 21

(c)

It is because the mass of A is larger than that of B.

22

1A

12. (a) (b) (c)

An a.c. voltmeter should be used.

1A

It is because transformers work at a.c. only. Z (i) X 1100 (ii) Total energy consumed = 2 × = 2.2 kW h 1000 Cost = $0.9 × 2.2 = $1.98

1A 1A 1A

(iii)

(d)

Output power = input power × efficiency 1100 Input power = = 1375 W 0.8 P Ip = V 1375 = = 6.25 A 220

For constant power transmitted, by P = IV , high voltage transmitted means reduced current flowing in the transmission line. N p Vp I s = = , the secondary current is much smaller than ( OR: By N s Vs I p the primary current if voltage is stepped up.) Then by P = I2R, ( where R is the resistance of the transmission line ) the power loss in the transmission line can be much reduced. (For effective communication.)

13.

1A 1A

1A

1A

1A 1A 1C

(a)

(correct scales)

1A

(labelled axes and units)

1A

(correct data points)

1A

(correct curve)

1A

(b) (i) (ii)

(c) (i) (ii)

58 °C From t = 3 min to t = 5 min, the substance has both solid and liquid states.

1A

Energy loss to the surroundings = 30 × 2 × 60 = 3600 J

1M 1A

Latent heat of substance = Energy loss to the surroundings

1M

ml = 3600 3600 l = 0.05

= 72 000 J kg–1

1A

1A

Physics Paper II 23

Solution 1C 2C 3B 4A 5A 6A 7D 8B 9B 10 A

3

11 D 12 C 13 B 14 B 15 A 16 A 17 C 18 D 19 D 20 A

21 B 22 A 23 D 24 D 25 D 26 A 27 C 28 B 29 A 30 B

31 B 32 B 33 B 34 D 35 C 36 B 37 C 38 B 39 A 40 A

41 D 42 B 43 B 44 B 45 C 　 　 　 　 　 　

Let m be the mass of the pendulum. By conservation of energy Total energy at A = Total energy at B 1 1 2 m(1) + m(10)(1.6) = mv 2 2 2 2 0.5 + 16 = 0.5v v 2 = 33 v = 5.74ms −1

4

Statement (1) is correct Statement (2) is wrong Consider the following situation. 1 kg of liquid A at 10oC is mixed with 2 kg of liquid B at 30oC. It is given that the specific heat capacity of A and B are 1000 J kg-1 oC-1 and 2000 J kg-1 oC-1. Assume that there is no heat

loss to surroundings. Let T be the final temperature. Heat gained by A = Heat lost by B (1)(1000)(T – 10) = (2)(2000)(30 – T) 1000T – 10000 = 120000 – 4000 T 5000T = 130000 24

T = 26oC Temperature rise of A = 26 – 10 = 16oC Temperature drop of B = 30 – 26 = 4oC Therefore, temperature rise of A ≠ temperature drop of B. Statement (3) is wrong because the specific heat capacity c of the whole body is m1 c1 + m 2 c 2 m1 + m 2 .

10

If water bubbles out of the container, a smaller amount of energy will be required to boil away E a certain amount of water. By l = m , the measured specific latent heat will be smaller than the standard value. Resistance of the light bulb =

20

V 2 62 = = 9 Ω. P 4

6 Voltage across each light bulb = 2 = 3 V

Power dissipated by each light bulb =

V 2 32 = = 1W R 9

R 29

Consider vertical direction,

40 N

R + 40 = 100 80 N R = 60 N Hence, vertical forces are balanced. W = 100 N

Net force = 80 N

R 31

To prevent the block from sliding, f consider the forces along the plane, 25

W=6N

f + 2 = 6 sin 30o f=1N

R

To move the block up the slope at uniform f velocity F = f + 6 sin 30o W=6N F=1+3=4N

33

By conservation of momentum (1)(4) + (1.5)(-2) = (1 + 1.5)v v = 0.4 ms-1

39

S1P = 3 m

S2P =

32 + 4 2 = 5 m

Path difference at P = S2P – S1P =5–3 =2m = 2.5 λ Therefore, destructive interference occurs at P and the amplitude of the wave at P is 0.

40

Statement (1) is wrong because the power dissipated in the secondary circuit is increased, so the power supplied by the voltage source is increased. This causes an increase in the reading of the ammeter. 26

Statement (2) is wrong because the voltmeter reading depends on the voltage source and the turns ratio only. Statement (3) is correct since the voltage across the bulbs remain unchanged.

41

Lenz’s law states that an induced current always flow to oppose the movement which started it. Therefore, the magnet falls at a slower rate. Also, heat will be produced because a current is induced in the copper wire.

27