Ep Exam Stuff > Eng Phys Exam 01

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 ………………………..

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.

For examiners' use only Q MC

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

6 Total

mark

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 An elastic collision conserves … A. B. C. D.

kinetic energy but not momentum, momentum but not kinetic energy, both momentum and kinetic energy, neither momentum or kinetic energy.

3 The mass number is … A. B. C. D.

the mass of a nuclei relative to that of 12C, the number of nucleons, A = N + Z, the mass of the nucleus, the number of protons in the nucleus, Z.

4 Special relativity often seems to be contrary to our intuition or common sense. This is because our everyday experiences in life are … A. B. C. D.

in inertial reference frames, all with electromagnetic radiation travelling at c, at much smaller velocities than the speed of light, all of the above.

5 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.

6 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.

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7 You are coming in to land your Kendell’s Airlines aircraft at Adelaide airport and hit a seagull flying in the opposite direction square in the middle of the pilot’s front window. Without all the gruesome details, the bird sadly was deceased and the window remained intact. We then know that, A. B. C. D.

the force of the bird on the glass was bigger than the force of the glass on the bird, the force of the bird on the glass was the same as the force of the glass on the bird, the force of the bird on the glass was less than the force of the glass on the bird, the aircraft didn’t slow down as it hit the bird.

8 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.

9 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.

10 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.

BONUS 11 The spectral distribution of x-rays exhibits a continuous distribution called the Bremmstralung (braking radiation) which is due to … A. B. C. D.

energy levels of the target atoms, the electron density of states of atoms in the anode, the nuclear force, electron interaction with the nucleus

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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.

Explain the difference between alpha (α), beta (β) and gamma (γ) radiation and how one could distinguish between them experimentally. ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ………………………………………………………………………………………………………………

2.

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 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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ENGINEERING PHYSICS JUNE 2001

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Two objects (widgits) of mass m1 and m2 are connected to each other via a light string over a pulley. The pulley has a radius R and a moment of inertia I about its axis of rotation. The string does not slip on the pulley and the system is released from rest. (a) Derive an expression for the linear speed of the masses as they pass each other. Hint: You can use either conservation of energy or the angular form of Newtons second law, F=ma. ………………………………………………………………………………………………

Pulley with moment of inertia, I

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R

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m1

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4.

A bungee jumper wishes to test the elasticity of their bungee rope. They attach a known weight of 20 kg to the end of the rope and measure a 1.0 m extension of the rope. If the bungee jumper weighs 75.0 kg, is 2.0 m tall and the bridge they wish to jump off is 50 m above a concrete highway, how long should the rope be if they wish to survive the experience? Hint: Calculate the spring constant of the rope. ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ………………………………………………………………………………………………………………

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For a short period the human body can withstand 5 g acceleration (that is a total force of 5 times their normal weight). The pilot goes into a vertical dive and pulls out before crashing.

(a) (b) (c)

Clearly label the diagram below (which is representative of this situation with the pilot in his seat) indicating all forces acting on the pilot at the very bottom of the dive. Express the magnitude of the centripetal force acting on the pilot at this point in terms of the pilots normal weight, w. With what radius of curvature may a pilot safely turn an aircraft upward at the end of a dive when their air speed is 800 km/hr? ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ………………………………………………………………………………………………

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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 16 seconds after it was released if we assume there is no 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.

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ENGINEERING PHYSICS JUNE 2001

7 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 = Fv W = F.s

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