Deck 3: Energy

Question 1

A rocket is fired in space.As it moves, the total momentum of the rocket and its exhaust gases

A)decreases.
B)remains the same.
C)increases.
D)Any of the choices could be correct, depending on the nature of the rocket.

Answer 1

remains the same.

Question 2

A spinning skater whose arms are at her sides then stretches out her arms horizontally.

A)She continues to spin at the same rate.
B)She spins more rapidly.
C)She spins more slowly.
D)Any of the choices could be correct, depending on how heavy her arms are.

Answer 2

She spins more slowly.

Question 3

The sun

A)attracts light waves passing nearby.
B)repels light waves passing nearby.
C)may attract or repel light waves passing nearby, depending upon the circumstances.
D)has no effect on light waves passing nearby.

Answer 3

attracts light waves passing nearby.

Question 4

Which one or more of the following is a vector quantity?

A)linear momentum
B)angular momentum
C)kinetic energy
D)potential energy
E)Both A and B

Question 5

The upper limit to the speed of an object with mass

A)depends on the mass.
B)corresponds to a KE equal to its rest energy.
C)is the speed of sound.
D)is the speed of light.

Question 6

If a spaceship 100 m long when at rest on the earth were to travel at nine-tenths the speed of light, its length as measured by an observer on the earth would be

A)0.
B)less than 100 m.
C)100 m.
D)more than 100 m.

Question 7

Which of the following is not a unit of work?

A)newton-meter
B)joule
C)kilogram-meter
D)watt-hour

Question 8

Rolling a ball up an inclined plank requires an amount of work proportional to the

A)horizontal distance the ball is shifted.
B)height the ball is raised.
C)sum of the horizontal distance the ball is shifted and the height the ball is raised.
D)length of the plank.

Question 9

To prevent it from tumbling in flight, a projectile such as a football is sent off spinning.The physical principle involved is

A)conservation of energy.
B)conservation of linear momentum.
C)conservation of angular momentum.
D)the first law of motion.

Question 10

The formula KE = ½mv² for kinetic energy

A)is the correct formula if v is properly interpreted.
B)always gives too high a value.
C)is the low-speed approximation to the correct formula.
D)is the high-speed approximation of the correct formula.

Question 11

Which of the following quantities is always the same to all observers?

A)time intervals
B)the speed of an object
C)the speed of sound
D)the speed of light

Question 12

A moving object must have which one or more of the following?

A)potential energy
B)kinetic energy
C)rest energy
D)momentum
E)Both B, C, and D

Question 13

When the speed of a moving object is halved,

A)its KE is halved.
B)its PE is halved.
C)its rest energy is halved.
D)its momentum is halved.

Question 14

The watt is a unit of

A)energy.
B)work.
C)momentum.
D)power.

Question 15

A golf ball and a ping-pong ball are dropped in a vacuum chamber.When they have fallen halfway down, they have the same

A)speed.
B)potential energy.
C)kinetic energy.
D)rest energy.

Question 16

A bowling ball rolling on level ground at the speed v strikes a basketball at rest.The basketball moves off in the original direction of the bowling ball

A)with the speed v while the bowling ball stops.
B)faster than v while the bowling ball continues slower than v.
C)with the speed v while the bowling ball moves backward.
D)together with the bowling ball at the same speed of less than v.

Question 17

When the momentum of a moving object is increased, there must also be an increase in which one or more of the following of the object's properties?

A)speed
B)acceleration
C)kinetic energy
D)potential energy
E)Both A and C

Question 18

According to the general theory of relativity, gravitation

A)acts only on moving bodies.
B)is really a general acceleration of the universe.
C)is a distortion in space-time.
D)is the same as in Newton's theory but is to be interpreted differently.

Question 19

What never changes when two or more objects collide is

A)the momentum of each object.
B)the kinetic energy of each object.
C)the total momentum of all the objects.
D)the total kinetic energy of all the objects.

Question 20

On a molecular level heat is

A)kinetic energy.
B)potential energy.
C)mass energy.
D)momentum.

Question 21

A ball whose momentum is mv strikes a wall and bounces off.The change in the ball's momentum is

A)0.
B)0.5 mv
C)mv
D)2 mv

Question 22

A horse has a power output of 1 hp (746 W) when it is pulling a cart.If the cart covers 100 m in 30 s, the force the horse exerts on the cart is

A)0.22 kN.
B)0.34 kN.
C)0.45 kN.
D)2.49 kN.

Question 23

A 90-kg llama has an average power output of 80 W.The minimum time the llama can go up a hill 500 m high is

A)9.4 min.
B)46 min.
C)1.5 h.
D)9.2 h.

Question 24

The work done in lifting 30 kg of bricks to a height of 20 m on a building under construction is

A)61 J.
B)600 J.
C)2940 J.
D)5880 J.

Question 25

A 1-N weight has a KE of 1 J when its speed is

A)0.45 m/s.
B)1 m/s.
C)1.4 m/s.
D)4.4 m/s.

Question 26

A 1-kg object is moving at 10 m/s.To double its kinetic energy, its speed should be increased to approximately

A)14 m/s.
B)15 m/s.
C)20 m/s.
D)40 m/s.

Question 27

A 1-N weight has a PE relative to the ground of 1 J when it is at a height of

A)10.2 cm.
B)1 m.
C)9.8 m.
D)98 m.

Question 28

A total of 4900 J is expended in lifting a 50-kg mass.The mass is raised to a height of

A)10 m.
B)98 m.
C)960 m.
D)245,000 m.

Question 29

The linear momentum of a 400-kg giraffe galloping at 5 m/s is

A)80 kgm/s.
B)2000 kgm/s.
C)5000 kgm/s.
D)19,600 kgm/s.

Question 30

The 2.5-kg head of an ax exerts a force of 80 kN as it penetrates 18 mm into the truck of a tree.The speed of the ax head when it strikes the tree is

A)1.2 m/s.
B)3.4 m/s.
C)34 m/s.
D)107 m/s.

Question 31

A 2-kg book is held 1 m above the floor for 50 s.The work done is

A)0.
B)10.2 J.
C)100 J.
D)980 J.

Question 32

A 1000-kg car whose speed is 80 km/h (22.2 m/s) has a kinetic energy of

A)25.2 kJ.
B)247 kJ.
C)2.42 MJ.
D)3.2 MJ.

Question 33

A horizontal force is applied to a 2-kg ball on a smooth table.The ball's speed is 8 m/s when it has gone 4 m.The magnitude of the force is

A)1.6 N.
B)2 N.
C)8 N.
D)16 N.

Question 34

The work you do in raising an orange from your waist to your mouth is roughly

A)1 J.
B)10 J.
C)100 J.
D)1,000 J.

Question 35

A 60-kg woman climbs a mountain 2000 m high in 10 h.Her average power output during the climb is

A)3.3 W.
B)33 W.
C)1960 W.
D)117.6 kW.

Question 36

The height above the ground of a child on a swing varies from 0.5 m at the lowest point to 2.0 m at the highest point.The maximum speed of the child is

A)about 5.4 m/s.
B)about 7.7 m/s.
C)about 29.4 m/s.
D)dependent on the child's mass.

Question 37

A 1-kg mass has a KE of 1 J when its speed is

A)0.45 m/s.
B)1 m/s.
C)1.4 m/s.
D)4.4 m/s.

Question 38

A 40-kg boy climbs a vertical ladder at 0.5 m/s.His power output is

A)5 W.
B)14 W.
C)20 W.
D)196 W.

Question 39

The speed of a 4000-kg truck whose KE is 1.8 MJ is

A)0.95 m/s.
B)30 m/s.
C)94 m/s.
D)900 m/s.

Question 40

A sedentary person requires about 6 million J of energy per day.This rate of energy consumption is equivalent to about

A)70 W.
B)335 W.
C)600 W.
D)250,000 W.

Question 41

The mass equivalent of 6.0 MJ is

A)6.7 * 10^-11 kg.
B)5.4 * 10^-9 kg.
C)6.7 * 10^-3 kg.
D)2.0 * 10^-2 kg.

Question 42

A 100-kg astronaut ejects 4 g of gas from her propulsion pistol at a speed of 50 m/s.Her recoil speed is

A)0.2 mm/s.
B)2 mm/s.
C)2 cm/s.
D)20 cm/s.

Question 43

An 800-kg car moving at 80 km/h collides head-on with a 1200-kg car moving at 40 km/h in the opposite direction.If they stick together, the wreckage now has an initial speed of

A)8 km/h.
B)40 km/h.
C)56 km/h.
D)60 km/h.

Question 44

An 800-kg car moving at 80 km/h overtakes a 1200-kg car moving at 40 km/h in the same direction.If the two cars stick together, the wreckage has an initial speed of

A)8 km/h.
B)40 km/h.
C)56 km/h.
D)60 km/h.

Question 45

When a ton of coal burns, it loses 3.3 * 10^-7 kg of mass.The energy given off is

A)3.7 * 10^-24 J.
B)3.3 * 10^-7 J.
C)100 J.
D)3.0 * 10¹⁰ J.

Question 46

An 800-kg car moving at 80 km/h collides head-on with a 1200-kg car moving at 40 km/h in the opposite direction.The total kinetic energy lost by the cars is

A)0.
B)less than that lost by the cars in question 48.
C)the same as that lost by the cars in question 48.
D)more than that lost by the cars in question 48.

Question 47

In bright sunlight, a solar cell with an efficiency of 20% might have a power output per square meter of

A)2 W.
B)20 W.
C)200 W.
D)2000 W.