PAPER 1 MAY 2014 Solutions TZ2

1. Which of the following is a unit of energy?

A. kg m–1 s–1

B. kg m2 s–2

C. kg m s–2

D. kg m2 s–1

Sample Energy → Kinetic → ½ mv2→

1

2(𝑘𝑔) 𝑚𝑠−1 2

→ (𝑘𝑔)𝑚2𝑠−2

2. Each side of a metal cube is measured to be 2.0 cm ±0.20 cm. What is the absolute uncertainty in

the calculated volume of the cube?

A. ±0.08 cm3

B. ±0.60 cm3

C. ±0.80 cm3

D. ±2.4 cm3

2.0 ± 0.2 = 2.0 ±0.2

2.0× 100% = 2.0 ± 10%

𝑉 = 𝑠3 = 2.0 ± 10% × 2.0 ± 10% × 2.0 ± 10% = 8 ± 30%

= 8 ± 8 × 0.3 = 8 𝑐𝑚3 ± 𝟐. 𝟒𝒄𝒎𝟑

3. A particle accelerates from rest. The graph shows how the acceleration a of the particle varies with time t.

What is the speed of the particle at t = 6.0 s?

A. 0.5 m s–1

B. 2.0 m s–1

C. 9.0 m s–1

D. 18 m s–1

The area under the curve of an acceleration vs. time

is equal to the speed.

𝐴 =1

2𝑏ℎ =

1

26 𝑠 3

𝑚

𝑠2= 9

𝑚

𝑠

4. A block slides down an inclined plane at constant speed.

Which diagram represents the free-body diagram of

the forces acting on the block?

Constant speed → 0 acceleration

0 acceleration → Sum of forces = 0

Sum of forces = 0 → Sum of the vectors = 0

Cancels each other out

Sum not 0

Sum not 0Sum not 0

Sum is 0

5. In the collision between two bodies, Newton’s third law

A. only applies if momentum is conserved in the collision.

B. only applies if energy is conserved in the collision.

C. only applies if both momentum and energy are conserved in the collision.

D. always applies.

Newton’s 3rd Law: For every action, there is an equal and opposite reaction.

6. A ball X moving horizontally collides with an identical ball Y that is at rest.

X strikes Y with speed v.

What is a possible outcome of the collision?

Transfer all

Momentum,

Perfect elastic

Collision.

2x the momentum

As before the collision

Net momentum after is 0.

Net momentum after is 0.

7. A ball is moving horizontally and strikes a vertical wall from which it rebounds horizontally.

The sketch graph shows how the contact force F between ball and wall varies with time of contact t.

The maximum value of F is F0 and the total time of

contact between ball and wall is T. What is the change

in momentum of the ball?

Dp = FDt = ½ F0 T

8. An insect of mass m jumps vertically from rest to a height h. The insect releases the energy needed for the jump in time Δt. What is the estimate for the power developed by the insect?

Power = Work / time = Force x distance /time = mgh/Dt

9. Two particles, X and Y, are attached to the

surface of a horizontally mounted turntable.

The turntable rotates uniformly about a vertical

axis. The magnitude of the linear velocity

of X is v and the magnitude of its acceleration

is a. Which of the following correctly compares

the magnitude of the velocity of Y and the

magnitude of the acceleration of Y with v

and a respectively?

Linear velocity = 2pr/t → For Y, the radius increased but everything else stays the same → greater than v

Acceleration is inward = v2/r → increase in v is squared where as increase in r is added → greater than a

10. Two objects are in thermal contact. For there to be no net transfer of thermal energy between the objects they must

A. have the same thermal capacity and be at the same temperature.

B. have the same thermal capacity only.

C. have the same mass and be at the same temperature.

D. be at the same temperature only.

Any difference in the temperature would imply heat transfer by conduction.

11. The specific latent heat is the energy required to change the phase of

A. one kilogram of a substance.

B. a substance at constant temperature.

C. a liquid at constant temperature.

D. one kilogram of a substance at constant temperature.

Substance Freezing

Point (K)

Heat of Fusion

(kJ/kg)

Boiling Point

(K)

Heat of

Vaporization (kJ/kg)

Hydrogen 13.8 58.6 20.3 452

Oxygen 54.4 138 90.2 213

Nitrogen 63.3 25.5 77.3 201

Ethyl Alcohol 156 104 351 858

Mercury 234 11.3 630 293

Water 273 334 373 2256

Lead 600 24.7 2023 871

Aluminum 932 396 2740 10465

Gold 1336 64.5 2933 1578

Copper 1359 134 1460 5065

Iron 1808 289 3023 6363

Latent heat chart

Constant temperature

12. An ideal gas is contained in a thermally insulated cylinder by a freely moving piston.

The gas is compressed by the piston and as a result the temperature of the gas increases. What is the explanation for the temperature rise?

A. The rate of collision between the molecules increases.

B. Energy is transferred to the molecules by the moving piston.

C. The molecules of the gas are pushed closer together.

D. The rate of collision between the molecules and the walls of the cylinder increases.

Since no thermal energy is transferred into the cylinder, the energy must come from an outside source, the piston. The piston colliding with the molecules increases the speed of the molecules. The increase in speed is the cause of the temperature increase.

13. A particle P executes simple harmonic motion (SHM) about its equilibrium position Y.

The amplitude of the motion is XY.

At which of the positions shown on the diagram is the acceleration of P equal to zero and the

kinetic energy of P equal to zero?

Think of it as a friction pendulum where the middle position of

the bob is Y and the end is X. Acceleration changes direction

when the bob is in the middle, there a = 0 at Y

Velocity = 0

KE = 0The yellow arrow

shows the acceleration.

14. A particle executes simple harmonic motion (SHM) with period T. Which sketch graph correctly shows how the total energy E of the particle varies with time t from t = 0 and t = T/2?

The total energy of the simple harmonic motion

is the sum of KE and PE. Since the PE converts to

KE and vice versa, the sum stay constant.

15. In which of the following systems is it desirable that damping should be as small as possible?

A. Suspension bridge

B. Quartz oscillator

C. Car suspension

D. Airplane/aeroplane wing

Dampening decreases the amount of vibrations. We would want dampening on bridges, cars, and wings to decrease the chance of damage to the parts.

16. The diagram shows, at a particular instant in time, part of a rope along which a wave is travelling.

The wave is travelling from left to right.

Which arrow shows the direction of motion of the rope at the point shown?

A. W

B. X

C. Y

D. Z

From the picture of this PHet simulation,

the string is below the equilibrium line

and in order to be above the equilibrium

line, it has to go up.

17. Which of the following is a statement of Ohm’s law?

A. The resistance of a conductor is constant.

B. The current in a conductor is inversely proportional to the potential difference across the

conductor provided the temperature is constant.

C. The resistance of a conductor is constant provided that the temperature is constant.

D. The current in a conductor is proportional to the potential difference across it.

The German Ohm studied resistance of materials in the 1800s and in 1826 stated:

“Provided the temperature is kept constant, the resistance of very many materials is constant over a wide range of applied potential differences, and therefore the potential difference is proportional to the current.”

18. Three identical filament lamps W, X and Y are connected in the circuit as shown. The cell has

negligible internal resistance.

When the switch is closed, all the lamps light.

Which of the following correctly describes what

happens to the brightness of lamp W and lamp

Y when the switch is opened?

When the switch is closed, the current in W is

is equal to the sum of the current at X and Y,

making W brighter than X and Y.

When the switch is opened, the current in W is

equal to the current in Y making them equally

bright. The current is decreased in W and

increased in Y so W got dimmer and Y got

brighter than when the switched was closed.

19. An electron is travelling in a region of uniform magnetic field. At the instant shown, the electron is moving parallel to the field direction.

The magnetic force on the electron is

A. upwards.

B. downwards.

C. to the right.

D. zero.

The magnitude of the force is F = qvB sinθ where θ is the angle < 180 degrees between the velocity and

the magnetic field. This implies that the magnetic force on a stationary charge or a charge moving parallel to

the magnetic field is zero, F = qvBsin(0o) = 0.

20. The gravitational field strength at a point X in a gravitational field is defined as the force

A. per unit mass on a mass placed at X.

B. on a mass placed at X.

C. per unit mass on a small point mass placed at X.

D. on a small point mass placed at X.

The gravitational field strength g is the force per unit mass acting on m due to the presence of M. (Slide 14 of 6.2)

21. Four point charges of equal magnitude W, X, Y

and Z are each fixed to a corner of a square.

W is a positive charge and X is a negative charge.

The arrow shows the direction of the

resultant electric field at the center of the square.

What are the correct signs of charge Y and of

charge Z?

Electric field rule is a test charge moves away from a

positive charge and towards a negative charge. Since the

arrow is pointing towards Y, it’s a negative charge. If X is

negative, then it will pulls the test charge towards it, but it

is not moving towards X, therefore, Z must be pulling it in

the opposite direction. This makes Z also negative.

22. Which of the following provides evidence for the existence of atomic energy levels?

A. Absorption spectra

B. Nuclear fission

C. The Geiger–Marsden experiment

D. Radioactive decay

Absorption and Emission Spectrum shows the different wavelength being absorbed or emitted. This shows the different energy levels of different elements.

23. What is the definition of the unified atomic mass unit?

define the unified atomic mass unit (u) using a neutral carbon-12 atom as our standard of precisely 12.000000 u.

24. Nuclei of the isotope nitrogen-14 are bombarded with neutrons and as a result nuclei of an isotope of carbon are produced. The nuclear reaction equation for this process may be written a

What is the nucleon number A of the isotope of carbon?

A. 12

B. 13

C. 14

D. 15

A = 14 to balance the equation

pCnN A 1

16

1

0

14

7 +→+

25. Degraded energy is energy that is

A. produced by the combustion of fossil fuels.

B. no longer available to perform useful work.

C. produced by low-energy density fuels.

D. relatively cheap to produce.

Degraded energy is energy lost to environment during energy transfer process usually is heat to the surrounding and is useless for energy production.

26. A black body has absolute temperature T and surface area A. The intensity of the radiation emitted by the body is I. Another black body of surface area 2A has absolute temperature 2T. What is the intensity of radiation emitted by this second black body?

A. 4I

B. 8I

C. 16I

D. 32I

( )( )

4

4

4

4

32

162

22

/

ATeP

TAeP

TAeP

ATeP

API

=

=

=

=

=

32 x the intensity over the same area.

27. In the production of energy from nuclear fission, fuel enrichment means increasing, in the fuel rods, the amount of

A. uranium-238.

B. plutonium-239.

C. uranium-235.

D. uranium-235 and plutonium-239.

28. In a wind generator, the kinetic energy of the wind cannot be completely converted into mechanical kinetic energy. This is because

A. momentum is not conserved in the collisions between air molecules and the blades.

B. the density of the air depends on the temperature of the air.

C. the air molecules cannot be brought completely to rest in collisions with the blades.

D. the wind speed does not remain constant.

The air constantly moving through the blades and coming in contact for a short period of time. Only a portion of the kinetic energy from the wind is used to turn the turbine and converted to electricity.

29. The greenhouse effect can be explained by the fact that the infrared radiation emitted by the surface of Earth

A. is absorbed by the atmosphere and then re-radiated in all directions.

B. raises the temperature of the upper atmosphere.

C. is trapped by the upper atmosphere.

D. is absorbed by the atmosphere and then all of it is re-radiated back to the surface of Earth.

Slide 45 and 46 Unit 82 Absorption of infrared radiation by greenhouse gases.

30. Which of the following mechanisms will not increase the rate of global warming?

A. The reduction in area of the ozone layer

B. The reduction of carbon dioxide solubility in the oceans

C. Deforestation

D. The melting of snow and ice at the poles