# Questions on Phenomenon of Physics

Physics Test 2

______1. In which one of the following situations will there be an increase in kinetic energy?

a. A projectile approaches its maximum height.

b. A box is pulled across a rough floor at constant speed.

c. A child pushes a merry go round causing it to rotate faster.

d. A satellite travels in a circular orbit around the earth at fixed altitude.

e. A stone at the end of a string is whirled in a horizontal circle at constant speed.

_____2. A roller coaster starts from rest at the top of a hill 18.0 m high. The car travels to the bottom of the hill and continues up the next hill, which is 10.0 m high. About how fast is the car moving at the top of the 10.0 m hill if friction is ignored?

a. 6.4m/s

b. 8.1m/s

c. 13 m/s

d. 18m/s

e. 27 m/s

_____3. In which one of the following situations is linear momentum not conserved?

a. A bomb suspended by a string explodes into one hundred fragments.

b. A bowling ball collides with ten pins.

c. A golf ball is struck by a club.

d. An astronaut floating in space throws a hammer away and subsequently moves in the opposite direction.

e. A tree limb is struck by lightning and falls to the ground.

_____4. A 50.0 kg boy runs at a speed of 10.0 m/s and jumps onto a cart. The cart is initially at rest. If the speed of the cart with the boy on it is 2.5 m/s, what is the mass of the cart?

a. 150kg

b. 175 kg

c. 210 kg

d. 260 kg

e. 300 kg

_____5. Consider the following three objects, each of the same mass and radius: (1) a solid sphere, (2) a solid disk, and (3) a hoop. All three are released from rest at the top of an inclined plane. The three objects proceed down the incline undergoing rolling motion without slipping. In which order do the objects reach the bottom of the incline?

a. 1,2,3

b. 2,3,1

c. 3,1,2

d. 3,2,1

e. All three reach the bottom at the same time.

____6. A cable stretches by an amount d when it supports a crate of mass M. The cable is then cut in half. If the same crate is supported by either half of the cable, by how much will the cable stretch?

a. d

b. d/2

c. d/4

d. 2d

e. 4d

_____7. A mass of 2.0 kg is attached to a spring with a spring constant of k = 300 N/m, as in the figure. The mass is pulled from its equilibrium position and released. Ignoring friction, what is its approximate frequency of oscillation?

a. 12

b. 0.5

c. 0.01

d. 1.9

e. 0.08

_____8. A guitar string is plucked and set into vibration. The vibrating string disturbs the surrounding air, resulting in a sound wave. Which entry in the table below is correct?

wave in the string sound wave in air

a. The wave is transverse, yes yes

b. The wave is longitudinal, yes yes

c. The wave is transmitted by particle vibration. no yes

d. The wave transports energy. yes no

_____9. A source moving through water at 10 m/s generates water waves with a frequency of 5.0 Hz. The speed of these water waves relative to the water surface is 20 m/s. The source approaches an observer who is at rest in the water. What wavelength would be measured for these waves by the stationary observer?

a. m

b. 2.Om

c. 4.Om

d. 6.Om

e. 8.Om

____10. A 4 m long string, clamped at both ends, vibrates at 200 Hz. If the string resonates in six segments, what is the speed of transverse waves on the string?

a. l00m/s

b. 133 m/s

c. 267 m/s

d. 328 m/s

e. 400 m/s

Part B: Short Answer Essay

Answer each question with 3-4 complete sentences. (20 points)

1. Standing waves are "interferences in space", where beats are "interferences in time". What does this mean?

2. How does temperature affect the pitch/frequency of organ pipes?

3. Can an object have momentum without kinetic energy? Can it have kinetic energy without momentum?

4. If suddenly everyone on the Earth were to suddenly vacation near the equator at the same time, how would this affect the length of the day?

Part C: Problems

Solve the following problems and show all of your work and calculations. You are graded as much on your methods as on the answers you give.

1. A 9.0 kg box of oranges slides from rest down a frictionless incline from a height of 5.0 m. A constant frictional force, introduced at point A, brings the block to rest at point B, 19 m to the right of point A. What is the coefficient of kinetic friction mk of the surface from A to B?

2. Pipe A is 0.5 m long and open at both ends. Pipe B is open at one end and closed at the other end. Determine the length of B so that is has the same fundamental frequency as A.

3. In the game of billiards, all the balls have approximately the same mass, about 0.17 kg. In the figure, the cue ball strikes another ball such that it follows the path shown. The other ball has a speed of 1.5 m/s immediately after the collision. What is the speed of the cue ball after the collision?

4. In a certain clock, a pendulum of length L1 has a period of T1 = 0.95 s. The length of the pendulum is adjusted to a new value L2 such that T2 = 1.0 s. What is the ratio L2 / L1?

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#### Solution Preview

Please see the attached file.

131756

______1. In which one of the following situations will there be an increase in kinetic energy?

a. A projectile approaches its maximum height.

b. A box is pulled across a rough floor at constant speed.

c. A child pushes a merry go round causing it to rotate faster.

d. A satellite travels in a circular orbit around the earth at fixed altitude.

e. A stone at the end of a string is whirled in a horizontal circle at constant speed.

The kinetic energy is given by

KE = ½ mv2

Hence the kinetic energy of the body (of constant mass) will increase only if magnitude of velocity (or speed) increases. This happens only in the situation given in 'c'. As the child pushes marry go round it rotates faster, its angular velocity and hence its speed (v=r) increases. This results in increase in kinetic energy.

Answer: c. A child pushes a merry go round causing it to rotate faster.

_____2. A roller coaster starts from rest at the top of a hill 18.0 m high. The car travels to the bottom of the hill and continues up the next hill, which is 10.0 m high. About how fast is the car moving at the top of the 10.0 m hill if friction is ignored?

a. 6.4m/s

b. 8.1m/s

c. 13 m/s

d. 18m/s

e. 27 m/s

This can be done using conservation of mechanical energy as there in no resistive (non conservative) force to be considered.

Gain in KE = loss in gravitational potential energy

Or ½ mv2 = mgh1 - mgh2

Gives v2 = 2*g*(h1 - h2) = 2*9.8*(18.0 - 10.0) = 156.8

Or v = 12.52 m/s

Answer: C. 13 m/s

_____3. In which one of the following situations is linear momentum not conserved?

a. A bomb suspended by a string explodes into one hundred fragments.

b. A bowling ball collides with ten pins.

c. A golf ball is struck by a club.

d. An astronaut floating in space throws a hammer away and subsequently moves in the opposite direction.

e. A tree limb is struck by lightning and falls to the ground.

According to law of conservation of linear momentum "If no external force is acting on the system, the linear momentum of the system remains conserved." Hence if an external force is acting on the system, the momentum will not be conserved.

In the situation C the golf ball is struck by a club but the club is pushed by the golfer or the external force is acting on the club and hence the momentums of the club ball system will not remains conserved.

(in situation e the photons in lighting carries momentum and that momentum is imparted to the tree limb)

Answer: c. A golf ball is struck by a club.

_____4. A 50.0 kg boy runs at a speed of 10.0 m/s and jumps onto a cart. The cart is initially at rest. If the speed of the cart with the boy on it is 2.5 m/s, what is the mass of the cart?

a. 150kg

b. 175 kg

c. 210 kg

d. 260 kg

e. 300 kg

If m be the mass of the cart then the initial momentum of the cart boy system

P1 = 50.0*10.0 + m*0 = 500.0 kg m/s.

The final momentum of the system will be

P2 = (50.0 + m)*2.5

Hence according to law of conservation of momentum we have

P2 = P1

Or (50.0 + m)*2.5 = 500.0

Gives m = 150 kg

Answer: a. 150 kg

_____5. Consider the following three objects, each of the same mass and radius: (1) a solid sphere, (2) a solid ...

#### Solution Summary

The solution contains explanations and solutions for number of multiple choice questions and problems of various phenomenon of physics such as interferences, oscillation, force, energy, momentum, rotation, force constant, springs, vibrations, string, sound, collisions, Doppler's-effect, resonance, waves, standing, pendulum, frequency, friction, beats.