Deck 3: Energy

Question 1

When a skater pulls in her arms to turn faster, her angular momentum

A) increases.
B) decreases.
C) remains the same.
D) Any of these choices, depending on circumstances.

Answer 1

remains the same.

Question 2

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.

Answer 2

1 J.

Question 3

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.

Answer 3

less than 100 m.

Question 4

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 5

On a molecular level heat is

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

Question 6

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 7

In the formula E₀ = mc², the symbol c represents the speed of

A) an object of mass m.
B) the observer.
C) sound.
D) light.

Question 8

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.

Question 9

An object that has linear momentum must also have

A) acceleration.
B) angular momentum.
C) kinetic energy.
D) potential energy.

Question 10

The watt is a unit of

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

Question 11

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 12

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.

Question 13

When the speed of an object is doubled,

A) its kinetic energy is doubled.
B) its potential energy is doubled.
C) its rest energy is doubled.
D) its momentum is doubled.

Question 14

A moving object does not necessarily have

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

Question 15

_7. 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

Which of the following is are) not a unit of power?

A) joule-second
B) watt
C) Newton-meter/second
D) horsepower

Question 17

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 18

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 19

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 20

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 21

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 22

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 23

A weightlifter raises a 200-kg barbell through a height of 2 m in 2.2 s. The average power he develops during the lift is

A) 0.18 kW.
B) 0.89 kW.
C) 1.78 kW.
D) 8.62 kW.

Question 24

The KE of a 900-kg car whose speed is 60 km/h is

A) 12.8 kJ.
B) 125 kJ.
C) 1.23 MJ.
D) 1.62 MJ.

Question 25

The minimum force that must be applied to a machine with a mechanical advantage of 5 in order to lift a 100-kg crate is

A) 20 N.
B) 196 N.
C) 500 N.
D) 4900 N.

Question 26

The speed of a 1000-kg car whose KE is 450 kJ is

A) 21 m/s.
B) 30 m/s.
C) 45 m/s.
D) 900 m/s.

Question 27

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 28

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 29

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 30

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 31

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 32

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 33

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 34

A 150-kg safe on frictionless casters is being raised 1.20 m to the bed of a truck using planks 4.00 m long. The force needed to push the safe up is

A) 441 N.
B) 450 N.
C) 500 N.
D) 1470 N.

Question 35

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 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 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 38

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 39

The mechanical advantage of a pair of scissors might be

A) 0.
B) 1/2.
C) 2.
D) -2.

Question 40

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 41

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 42

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 43

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 44

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 45

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 46

If a shell fired from a cannon explodes in midair,

A) its total momentum increases.
B) its total momentum decreases.
C) its total KE increases.
D) its total KE decreases.

Question 47

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.