Deck 6: Energy and Oscillations

Question 1

A mass hangs from a spring that is fixed to the ceiling. The mass is now pulled down and released so the mass oscillates up and down. Which of the following statements is true?

A) The kinetic energy of the oscillating mass is a constant.
B) Adding mass to the spring will make it oscillate faster.
C) The restoring force of the spring is equal to the weight of the mass.
D) The gravitational force on the mass oscillates at the same frequency as the mass.
E) None of these is true.

Answer 1

None of these is true.

Question 2

When work is done by a force on an object, then which of the following is true?

A) The speed of the object must change.
B) The object does an equal amount of work on the force.
C) The work done is equal to the change of total kinetic energy of the object plus any energy appearing as heat, light, or sound.
D) The object must change height above the ground.
E) The force cannot take energy away from the object.

Answer 2

The work done is equal to the change of total kinetic energy of the object plus any energy appearing as heat, light, or sound.

Question 3

For a 0.1-kg frog to jump to a height of 1.0 meter requires an energy of about

A) 10 Joule.
B) 1.0 Joule.
C) 0.5 Joule.
D) 0.1 Joule.

Answer 3

1.0 Joule.

Question 4

Which of the following is possessed by a moving object, but not by a stationary object?

A) Energy
B) Mass
C) Inertia
D) Kinetic energy

Question 5

A child riding on a swing rises to a height 1.0 m above the lowest point. Another child of equal mass whose speed at the lowest point is twice as great will rise

A) to a height which depends on the mass.
B) to the same height.
C) twice as high.
D) four times as high.

Question 6

Which of the following is not an energy unit?

A) N·m
B) Joule
C) Watt
D) calorie
E) kWh

Question 7

Virgil rides a skateboard (combined mass 100 kg) at 4 m/s, and Jill rides a bicycle (combined mass 64 kg) at 5 m/s.

A) Virgil has the greater kinetic energy.
B) Jill has the greater kinetic energy.
C) Virgil and Jill have equal kinetic energies.

Question 8

Jim exerts a force of 500 N against a 100-kg desk that does not move. Virgil exerts a force of 400 N against a 60-kg desk that moves 2 m in the direction of the push. Mik exerts a force of 200 N against a 50-kg desk that moves 5 m in the direction of the push. The most work is done by

A) Jim.
B) Virgil.
C) Mik.
D) Virgil and Mik, who do equal amounts of work.

Question 9

If work was done on an object, the object must have

A) changed only its direction of motion.
B) accelerated.
C) experienced a frictional force.
D) changed its position.

Question 10

Suppose you climb the stairs of an eight-story building, about 24 m high, and your mass is 70 kg. The gravitational potential energy you gain is about

A) 16,500 calories.
B) 40 calories.
C) 16,500 Joule.
D) 40 Joule.

Question 11

A brick slides across a horizontal rough surface and eventually comes to a stop. What happened to the kinetic energy of the brick?

A) Nothing; it is still in the brick but is now called potential energy.
B) It was converted to other energy forms, mostly heat.
C) It was converted to a potential energy of friction.
D) It was simply destroyed in the process of stopping.

Question 12

The power of an engine is a measure of

A) the rate at which it can perform work.
B) its volume.
C) its ability to outperform a horse.
D) the total amount of work it can perform.

Question 13

Initially, a blue automobile has twice the kinetic energy that a red automobile has. Both are braked to a stop; both have the same amount of braking force. The red auto will stop in ____________________ as the blue auto.

A) half the distance
B) the same distance
C) twice the distance
D) four times the distance
E) one fourth the distance

Question 14

A box is moved 10 m across by a floor a force of 25 N acting along the direction of motion. The work done by the force is

A) 250 J.
B) 125 J.
C) 35 J.
D) 25 J.
E) 2.5 J.

Question 15

A block sits on a slight incline, held at rest by the frictional force between the block and the incline. Which of the following statements is true?

A) The frictional force performs no work, since there is no motion of the block.
B) The work by the frictional force is equal to the gravitational potential energy of the block.
C) The work done by the frictional force is negative, since the force of friction opposes the direction that the block is being tugged by gravity.
D) The work done by gravity is entirely converted into heat because of the friction present.
E) None of these is true.

Question 16

An object with a kinetic energy of 40 J is stopped in a distance of 0.01 m. The average force that stops the object is

A) 40,000 N.
B) 4,000 N.
C) 400 N.
D) 40 N.
E) 0.4 N.

Question 17

A 3.0-kg cat runs to the left at 10 m/s and a 10-kg dog runs to the right at 4.0 m/s. The total kinetic energy is

A) -35 Joule.
B) 0.
C) -70 Joule.
D) 146 Joule.
E) 230 Joule.

Question 18

Which has the greater kinetic energy-a 1-ton car moving at 30 m/s or a half-ton car moving at 60 m/s?

A) The half-ton car
B) The 1-ton car
C) Both have the same kinetic energy.
D) It cannot be determined because the mass of the cars can't be found.

Question 19

A quarterback of mass 85 kg is running at 10 m/s. Also, a tackle of mass 100 kg is running at 9 m/s.

A) The tackle has the greater kinetic energy.
B) The quarterback and the tackle have equal kinetic energies.
C) The quarterback has the greater kinetic energy.

Question 20

A 20 N ball and a 40 N ball are dropped at the same time from a height of 10 meters. Air resistance is negligible. Which of the following statements is accurate?

A) After 1 second has elapsed, both balls have the same kinetic energy, since they have the same acceleration.
B) The heavy ball has a greater acceleration and falls faster.
C) Both balls hit the ground at the same time but gravity does more work on the heavy ball than on the light ball.
D) The light ball has a greater speed, since it can accelerate faster than the heavy ball.

Question 21

A box is pushed across a rough horizontal floor by a force acting parallel to the floor in the direction of motion. A force doing negative work on the body is

A) gravity.
B) the applied force.
C) friction.
D) the normal reaction force of the floor upward on the body.
E) a fictitious force.

Question 22

A refrigerator weighing 1500 N is to be lifted onto a truck bed that is 1.0 m above the ground. When pushed up a slanting ramp 2.0 m in length a force of only 750 N is required to move it at constant velocity. Comparing the work involved in lifting the refrigerator straight up to the work in pushing it along the ramp, there is

A) less work required when the ramp is employed.
B) more work required when the ramp is employed.
C) an equal amount of work is required in each case.

Question 23

A grandfather clock that is regulated by a pendulum is orbiting the Earth aboard the space station. Compared to an identical clock on Earth, the grandfather clock aboard the space station will

A) run fast.
B) keep time at the same rate.
C) run slow.
D) not run at all.

Question 24

Work is done on an object to increase its total energy. Which one of the following is true?

A) The total work done must be equal to the energy lost to heat and sound.
B) Both the kinetic energy and potential energy can be larger.
C) If the potential energy increases, then the kinetic energy must decrease.
D) The object must have a larger speed and smaller height above the ground.

Question 25

A pendulum swings through 10 cycles in 2 seconds. The frequency of the pendulum is

A) 10 Hz.
B) 5 Hz.
C) 2 Hz.
D) 0.5 Hz.
E) 0.1 Hz.

Question 26

A box is pushed across a rough horizontal floor by a force acting parallel to the floor in the direction of motion. A force doing no work during the motion is

A) the applied force.
B) gravity.
C) friction.
D) All of the forces are doing work.

Question 27

A painter of mass 70 kg climbs 3.0 m up a ladder. The painter's potential energy has increased by

A) 2058 J.
B) 1029 J.
C) 686 J.
D) 261 J.
E) 210 J.

Question 28

A ball at the end of a string is swinging as a simple pendulum. Assuming no loss in energy due to friction, we can say for the ball that

A) the potential energy is maximum at each end of the motion.
B) the mechanical energy changes and is maximum where the kinetic energy is minimum.
C) the mechanical energy changes and is maximum where the kinetic energy is maximum.
D) the kinetic energy does not change but the potential energy does.

Question 29

Which of the following is not a unit of power?

A) Watt
B) KiloWatt
C) Joule/second
D) KiloWatt-hour
E) Horsepower

Question 30

A grandfather clock that is regulated by a pendulum is taken to the Moon, where the acceleration of gravity is less. Compared to an identical clock on Earth, the grandfather clock on the Moon will

A) run fast.
B) keep time at the same rate.
C) run slow.

Question 31

A mass hangs on a spring held in a physicist's hand. When the mass is pulled down and then released, it oscillates with a period of 2.0 s. This system is taken to the space station orbiting the Earth. The spring is held in an astronaut's hand, and the mass, when pulled down and released, will

A) oscillate with a longer period.
B) oscillate with a shorter period.
C) oscillate with an unchanged period.
D) not oscillate at all.

Question 32

In order for a body to exhibit simple harmonic motion there must be

A) a constant force pushing the body away from the center.
B) a constant force drawing the body toward the center.
C) a force pushing the body away from the center and increasing with distance away from the center.
D) a force drawing the body toward the center and increasing with distance away from the center.
E) a force drawing the body toward the center and decreasing with distance away from the center.

Question 33

A worker in a warehouse uses a rope passing through some pulleys to lift a heavy crate. The worker exerts a force five times less than the weight of the crate but has to move the rope four times as far as the crate moves. This situation

A) can happen because the extra distance traveled makes up for the smaller force applied.
B) can happen because there is friction in the pulleys so the work done by the worker will not equal the work done on the crate.
C) cannot happen because a crate that heavy would lift the worker, rather than the worker lifting the crate.
D) cannot happen because the work done by the worker is less than the work done on the crate.

Question 34

The kinetic energy of a body is correctly given by which of the following expressions? (m=mass, v=speed)

A) mv
B) 2mv²
C) mv²
D) (½)mv²
E) (½)mv

Question 35

On a frictionless tabletop, a force is applied to an object: the object's velocity is horizontal and the force is perpendicular to the tabletop. Which of the following is true?

A) The applied force is friction.
B) The total energy of the object does not change.
C) There cannot be more than one force on the object.
D) The force does work on the object.

Question 36

A mass hangs on a spring held in a physicist's hand. When the mass is pulled down and then released, it oscillates with a period of 2.0 s. This system is taken to the Moon, where the acceleration of gravity is less. The spring on the Moon is held in an astronaut's hand, and the mass, when pulled down and released, will

A) oscillate with a longer period.
B) oscillate with an unchanged period.
C) oscillate with a shorter period.
D) not oscillate at all.

Question 37

If the speed of a car is doubled but the brakes apply the same force, the distance required to stop the car changes by a factor of

A) ¼.
B) ½.
C) 1.
D) 2.
E) 4.

Question 38

A bullet of mass 0.010 kg and speed of 500 m/s is brought to rest in a wooden block after penetrating a distance of 0.10 m. The work done on the bullet by the block is

A) -1250 J.
B) 1250 J.
C) -2.5 J.
D) 2.5 J.
E) zero.

Question 39

A body is suspended from a spring hanging vertically. The body is then pulled downward so the spring stretches. Consider the change in the elastic potential energy (EPE) of the spring and the change in gravitational potential energy (GPE) as the body is pulled down.

A) The GPE decreases while the EPE increases.
B) The GPE decreases but the EPE is unchanged.
C) The EPE increases but the GPE is unchanged.
D) The GPE increases along with the EPE.
E) Both the GPE and the EPE decrease.

Question 40

A box is moved 20 m across a smooth floor by a force making a downward angle with the floor, so that there is effectively a 10 N force acting parallel to the floor in the direction of motion and a 5 N force acting perpendicular to the floor. The work done is

A) 300 J.
B) 200 J.
C) 100 J.
D) 20 J.
E) 5.0 J.

Question 41

If the kinetic energy of an object increases, then

A) the potential energy must decrease.
B) the total energy must increase.
C) there can only be one force on the object.
D) the speed must increase as well.

Question 42

In pole-vaulting, in addition to gravitational potential energy there is potential energy in the bent pole which is analogous to potential energy stored in a _______________ under compression.

Question 43

A ball of mass 5 kg attached to a string is swung in a horizontal circle of radius 0.5 m. If the tension in the string is 10 N, the work done by the tension in one revolution is _____________ J.

Question 44

When a force acts in a direction opposite to the motion, __________ work is said to be done on the object.

Question 45

A simple machine allows you to move _________ masses even though you apply _________.

A) larger; smaller force over a longer distance
B) smaller; kinetic energy spread over the entire path
C) stationary but not moving; many Newtons of force
D) smaller; potential energy deficits

Question 46

A spring wound clock makes use of ____________ energy to drive the mechanism.

Question 47

Total mechanical energy of a system is conserved when there are only ___________________ forces doing work on the system.

Question 48

Other things being equal, the pole-vaulter having the greatest __________ energy prior to going into the jump should jump the highest.

Question 49

If an object has a larger potential energy than kinetic energy,

A) the speed of the object will increase.
B) the speed of the object will not change.
C) the speed of the object will decrease.
D) It is not possible to predict what the speed will be; it depends on the situation.

Question 50

The potential energy of a spring is 0.3 J when it is compressed 0.04 m to the left of its equilibrium position. At this point it comes to its leftmost position. What is its kinetic energy at this point?

A) -0.3 J
B) zero
C) 0.3 J
D) 375 N/m

Question 51

The potential energy of a spring is 0.3 J when it is compressed 0.04 m to the left of its equilibrium position. At this point it comes to its leftmost position. What is its kinetic energy when it returns to the equilibrium point?

A) 0.25 J and moving to the right
B) zero
C) -0.25 J and moving to the left
D) 0.25 J and at rest.
Fill in the Blank Questions

Question 52

The conversion of the initial potential energy of a person on a sled on a smooth icy slope into kinetic energy at the bottom is an example of the principle of conservation of _________________.

Question 53

Two springs are hung from a ceiling and carry identical masses. The first spring has a spring constant twice as large as the second spring. The masses on each spring are pulled down from their equilibrium positions the same distance and are then released. The amplitude of the oscillation is

A) the same for both springs.
B) larger for the first spring.
C) larger for the second spring.
D) It is not possible to know which is larger without knowing the mass.

Question 54

A small radio-controlled car's motor rated at 6 watts output is capable of performing _________________ Joules of work in 15 seconds.

Question 55

The __________ of a pendulum is the amount of time the pendulum takes for one full swing.

Question 56

When you lift a heavy 5.0 kg crate straight up from ground level to a height of 2.0 m above ground level, then you have changed the crate's gravitational potential energy by

A) 98 m²/s².
B) 98 J.
C) an undetermined amount, because it depends on how fast you lifted it.
D) 98 N.
E) 98 kg m/s.

Question 57

Can the gravitational force of Earth do positive or negative work on a geosynchronous communication satellite, once it is on its circular orbit?

A) No, because the satellite has zero acceleration.
B) No, because the force is always perpendicular to the orbital path.
C) Yes, because centripetal forces always do positive work.
D) Yes, because its speed is constant.

Question 58

A mass attached to a spring is drawn back 2 cm from equilibrium and released. If a second spring were used that had a smaller spring constant than the first but the mass was the same, which of the following would be larger?

A) Amplitude
B) Frequency
C) Period
D) Initial restoring force

Question 59

A horizontal force acts on a block that is initially at rest but free to move across a smooth horizontal surface. The work done by this force ___________ (increases; does not change; decreases) the kinetic energy of the block.