Ep Exam Stuff > Eng Phys Exam 02

UNIVERSITY OF SOUTH AUSTRALIA School of Electrical & Information Engineering (Applied Physics)

Semester 1 Examinations, June 2001

ENGINEERING PHYSICS (13385) Sections (D and E)

Name .....................................................................................Student ID ………………………..

For examiners' use only

INSTRUCTIONS TO CANDIDATES 1. Read carefully the directions for each section of this examination paper. 2. Write legibly on this examination paper which is to be submitted. 3. To speak to the supervisor, raise your hand.

Q MC 1 2

DO NOT REMOVE OR DESTROY ANY PART OF THIS PAPER, WHICH MUST BE SUBMITTED INTACT. EXAMINATION PAPERS MUST NOT BE REMOVED FROM THE EXAMINATION ROOM.

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TOTAL TIME for both Sections (D and E): 30 minutes

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ENGINEERING PHYSICS JUNE 2001

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SECTION A: MULTIPLE CHOICE QUESTIONS Recommended Time: 15 minutes General Instructions to Candidates 

All candidates must attempt this Section.



All questions are of equal value.

 Attempt ALL questions from this Section, and record your answers in the boxes provided on the right hand side of the paper.

1 If an object is thrown downward (rather than released from rest) its downward acceleration after release (in the absence of air resistance) is … A.

B. C. D.

less than 9.8 m/s2, 9.8 m/s2, greater than 9.8 m/s2, unknown due to insufficient information.

2 The mass of a frozen chicken on the surface of the moon is … A. B. C. D.

less than on earth, greater than on earth, the same as it is at sea level on the earth, less than on the top of Mt. Everest.

3 Two skydivers jump from the plane at the same instant in time. Skydiver A weighs twice as much as skydiver B and they both forget to put on their parachutes. Neglect air resistance, then which statement below is true? A. B. C. D.

Ski diver A hits the ground before B, Ski diver B hits the ground before A, They both hit the ground at the same time, There is insufficient information in this problem to enable one to determine the answer.

4 A pilot flies in a vertical circle at a constant speed great enough to feel weightless at the very top of the loop. Which of the following statements is true? A. B. C. D.

The centripetal force at the top is greater than that at the bottom, The normal force supplied by the pilots seat is larger at the bottom than at the top, The pilot would experience twice the gravitational field at the bottom of the loop, The mass of the pilot changes.

5 During a demonstration of power in a physics class, two students are asked to run up a flight of stairs as fast as they can. In the interests of gender balance and equality a male & female student of similar build was chosen. Computed results for their power output during these sprints show the female’s power was greater. Which of the following statements is true? A. B. C. D.

There must have been an error in the calculation, This is because the female ran fast enough that she did more work during the trial, This is because the female ran fast enough that she did her work in much less time, This is because women weigh less than men of the same size.

6 Which of the following has the larger moment of inertia? A. B. C. D.

A CD when it spins very fast, The same CD which is not rotating, The same CD with a stick on-label when it spins very fast, A DVD of the same size as the CD but has twice the mass.

7. A permanent ceramic magnet is composed of … A.

Diamagnetic material,

ENGINEERING PHYSICS JUNE 2001

B. C. D.

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Paramagnetic material, Ferromagnetic material, High temperature super-conducting material.

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SECTION B: QUESTIONS & PROBLEMS Recommended Time: 15 minutes General Instructions to Candidates 

All candidates must attempt this section and are to choose THREE questions to answer

 Attempt only THREE of the six questions/problems from this section, and record your answers in the  

1.

space provided. If you need extra space write on the back of the page and clearly indicate which question/problem the answer pertains to. Put a diagonal line through any questions/problems or parts thereof that you do not want to count towards your THREE answers. All questions/problems are of equal value and you should spend typically 5 minutes on each.

Suppose you are driving a car along the freeway at the speed limit (100 kph in South Australia). Why should you avoid slamming on the brakes if you want to stop in the shortest distance? That is, why should you keep the wheels turning as you brake? [This is the idea behind ABS or Anti-lock Braking Systems on modern cars] ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… When water freezes, it expands by about 9.00%. What would be the pressure change inside your car’s engine block if the water in it froze while you were on a ski trip to the Australian alps? The bulk modulus of ice is 2.0 x 109 N/m2. [Check you calculation for the correct number of significant figures] ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ………………………………………………………………………………………………………………

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A helicopter has a main blade of diameter 7.50 m which rotates at 450 r.p.m. and a tail blade of diameter 1.00 m which rotates at 3000 r.p.m. (a)

What is the speed of the tips of the tail rotor?

……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… If the main blade starts from rest with an angular acceleration of 10.5 rad s-2, calculate to the correct number of significant figures, (b)

the time it would take for the main blade to reach the angular velocity indicated above.

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Why do you think helicopters have two rotors? Explain.

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3. An energy efficient light bulb which consumes 26.0 W of electrical power can produce the same level of brightness (optical power) as a conventional filament bulb operating at 100 W power. The lifetime of the energy efficient bulb is 10,000 hours but costs $16.00 to purchase. The conventional bulb only lasts for 1,000 hours on average but only costs $0.80.

Determine the total savings obtained through the use of one energy efficient bulb over its lifetime as opposed to the use of conventional bulbs over the same period. Assume an energy cost of $0.0800 per kilowatt hour. ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ………………………………………………………………………………………………………………

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A person at an airport is towing their 20.0 kg suitcase at a constant speed by pulling on a strap at an angle of θ above the horizontal. They pull on the strap with a 35.0 N force and the frictional force on the case is 20.0 N.

(a) (b) (c)

Draw a free body diagram for the suitcase, i.e. clearly label the diagram below (which is representative of this situation) indicating all forces acting on the suitcase. What angle does the strap make with the horizontal. What normal force does the floor exert on the suitcase?

θ

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A 1 m3 crate of cargo weighing 100 kg is released from an aircraft during horizontal flight and its parachute fails to open. (a) (b)

How high was the aircraft flying if the cargo crate hits the ground 18.00 seconds after it was released if we assume there is no air resistance? If we do not ignore air resistance, does the crate reach terminal velocity before impact? Remember that the drag coefficient is 0.5 for spheres and up to 2 for odd shapes. Lets assume the drag coefficient is 1.00 for a cube and remember that an object reaches terminal velocity when the resistive force R is balanced by the gravitational force.

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ENGINEERING PHYSICS JUNE 2001

9 Semester 1 Examinations, June 2001

ENGINEERING PHYSICS (13385) FORMULAE & CONSTANTS vf = vi + at v f = v + 2as s = vit + ½ at2 2

2 i

w = mg PE = mgh KE = ½ mv2 ω = ωi + αt ω 2 = ω i2 + 2αθ

embed Equation.2 EMBED Equation mm F =G 12 2 r mm EMBED Equation U = −G 1 2 r 1 R = DρAv 2 2 F Y = A ∆ 

θ = ωit + ½ αt2

 I SIL = 10 log  I0

y = ym sin(kx ± ωt)

 v ± v0   f ' = f   v  vs 

x = A cos(ωt + φ) k = 2π/λ , f = 1/T v = fλ ω = 2πf a = −ω2x L = Iω F = ma

Icylinder = ½ mR2 Isphere = 2/5 mR2 Ihoop = mR2 T = 2π

k .x m

P = τω

I ∝ 1/d2 Io = 10-12 W/m2

aT = αr ac = ω2r = v2/r Fc = m v2/r τ = Fr sin θ τ = Iα L = Iω = mvr Krot = ½ Iω2 p = mv P = dW/dt = F.v W = F.s = Fs cos θ

hollow cylinder, hoop

Fs = −kx a = −

v = ωr

solid cylinder, disc

 g

W = τθ s = θr

  

Earth Radius 6.37 x 106 m Earth Mass 5.98 x 1024 kg Moon Radius 1.74 x 106 m Moon Mass 7.36 x 1022 kg Earth-Moon Distance 3.84 x 108 m Speed of light c = 3 x 108 ms-1 Speed of sound in air v = 330 ms-1 Density of air (STP) ρ = 1.29 kg m-3 Gravitational constant G = 6.67 x 10-11 Nm2kg-2 Acc’n due to gravity g = 9.81 ms-2 Electron mass me = 9.109 x 10-31 kg Proton mass mp = 1.673 x 10-27 kg Elementary charge e = 1.602 x 10-19 C Planck’s constant h = 6.626 x 10-34 Js