Deck 3: Energy and Conservation Laws

Question 1

Kinetic energy is conserved in elastic collisions.

Answer 1

True

Question 2

The energy of a ball rolling up an inclined plane is an example of both kinetic and gravitational potential energy.

Answer 2

True

Question 3

Conservation laws can be used even when the details of what is occurring inside a system aren't known.

Answer 3

True

Question 4

The energy of a body moving across a horizontal surface is an example of kinetic energy.

Question 5

The energy stored in a pile driver is an example of gravitational potential energy.

Question 6

Consider a situation where a skater pulls her arms inward, causing her rotation rate to speed up.
Linear momentum is not conserved.

Question 7

The energy stored in a stretched spring is an example of gravitational potential energy.

Question 8

Consider a situation where two moving objects collide and rebound from each other.
Linear momentum is definitely conserved.

Question 9

Linear momentum is conserved in all collisions.

Question 10

Consider a situation where a skater pulls her arms inward, causing her rotation rate to speed up.
Angular momentum is conserved.

Question 11

Work done within an isolated system can increase the energy of the system.

Question 12

Consider a situation where two moving objects collide, stick to each other, and move off together.
Kinetic energy is definitely not conserved.

Question 13

The momentum of an object never changes.

Question 14

The energy in the water at the top of a waterfall is an example of gravitational potential energy.

Question 15

Consider a situation where two moving objects collide and rebound from each other.
Kinetic energy is definitely conserved.

Question 16

Consider a situation where a skater pulls her arms inward, causing her rotation rate to speed up.
Kinetic energy is conserved.

Question 17

Consider a situation where two moving objects collide, stick to each other, and move off together.
Linear momentum is definitely conserved.

Question 18

Momentum is conserved only when there is no friction.

Question 19

Centripetal force changes linear momentum but not angular momentum.

Question 20

For a body oscillating at the end of a spring,the energy is only elastic potential energy.

Question 21

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t.
The linear momentum of the crate is Fv.

Question 22

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t.
The work you do on the crate is Fv.

Question 23

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t.
The power you supply to the crate is Fd/t.

Question 24

If the velocity of an aircraft is doubled,the kinetic energy of the aircraft is also doubled.

Question 25

A watt is equal to 746 horsepower.

Question 26

Consider a situation where you carry a 20-N box up a flight of stairs, raising its elevation by 5 m.
When the box hits the floor its kinetic energy is converted into internal energy.

Question 27

A spacecraft can gain energy by passing near a planet.

Question 28

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t.
The kinetic energy of the crate is 1/2 mv².

Question 29

When more people ride upward in an elevator,more power is required.

Question 30

A person runs up a long flight of stairs in 10 seconds.If the person's weight is 600 N and the vertical height of the stairs is 20 meters,the person's power output is 1,200 W.

Question 31

Consider a situation where you carry a 20-N box up a flight of stairs, raising its elevation by 5 m.
You drop the box.As it falls to its original level,its kinetic energy is 100 J.

Question 32

Consider a situation where you carry a 20-N box up a flight of stairs, raising its elevation by 5 m.
The work you do is 4 J.

Question 33

Consider a situation where you carry a 20-N box up a flight of stairs, raising its elevation by 5 m.
The increase of potential energy of the box is 100 J.

Question 34

The collision between two cars in an accident is an inelastic collision.

Question 35

When a car comes to a stop its kinetic energy is converted to internal energy in its brakes,heating them up.

Question 36

The measure of a body's resistance to being rotated is its angular momentum.

Question 37

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t.
The potential energy of the crate is mgd.

Question 38

A rocket can never go faster than the speed of its exhaust.

Question 39

A 2 kg car moving towards the right at 4 m/s collides head on with an 8 kg car moving towards the left at 2 m/s,and they stick together.After the collision,the velocity of the combined bodies is 0.8 m/s pointing towards the left.

Question 40

You carry a 20-N box 5 m horizontally across a room.The work you do is 100 N-m.

Question 41

Consider a situation where a skater pulls her arms inward, causing her rotation rate to speed up.
Angular momentum

A)is definitely conserved.
B)is definitely not conserved.
C)may or may not be conserved.
D)none of the above

Question 42

Consider a situation where two moving objects collide, stick to each other, and move off together.
Kinetic energy

A)is definitely conserved.
B)is definitely not conserved.
C)may or may not be conserved,depending on the nature of the collision.
D)none of the above

Question 43

Consider a situation where two moving objects collide and rebound from each other.
Linear momentum

A)is definitely conserved.
B)is definitely not conserved.
C)may or may not be conserved,depending on the nature of the collision.
D)none of the above

Question 44

Consider a situation where two moving objects collide and rebound from each other.
Kinetic energy

A)is definitely conserved.
B)is definitely not conserved.
C)may or may not be conserved,depending on the nature of the collision.
D)none of the above

Question 45

Consider a situation where two moving objects collide, stick to each other, and move off together.
Linear momentum

A)is definitely conserved.
B)is definitely not conserved.
C)may or may not be conserved,depending on the nature of the collision.
D)none of the above

Question 46

Consider a situation where two moving objects collide, stick to each other, and move off together.
Internal energy

A)remains constant.
B)decreases.
C)increases.
D)varies but in a way that cannot be predicted.

Question 47

Which of the following is not an example of potential energy?

A)The energy stored in a pile driver.
B)The energy stored in a stretched spring.
C)The energy of a body moving across a horizontal surface.
D)The energy in the water at the top of a waterfall.

Question 48

Kinetic energy is conserved in

A)an inelastic collision.
B)an elastic collision.
C)any collision where two objects rebound off each other.
D)none of the above.

Question 49

The linear momentum of a truck will be greater than that of a bus if

A)the truck's mass is larger than the bus's but its speed is the same.
B)the truck's speed is larger than the bus's but its mass is the same.
C)the truck's mass and speed are both larger than the bus's.
D)any of the above.

Question 50

If a force on an object is aimed in the direction of the object's velocity,the force does

A)no work.
B)positive work.
C)negative work.
D)any of the above.

Question 51

What does it mean for a physical quantity in a system to be conserved?

A)It is used in the most efficient manner possible.
B)It stays in its original state forever.
C)The total amount of it in the system stays constant.
D)none of the above.

Question 52

If a force on an object is aimed perpendicular to the direction of the object's velocity,the force does

A)no work.
B)positive work.
C)negative work.
D)any of the above.

Question 53

What are the SI units of momentum?

A)kg m/s
B)pascals
C)joules
D)watts

Question 54

A barrel rolling down an inclined ramp has only kinetic energy.

Question 55

Work is done on an object when

A)it moves in a circle at constant speed.
B)it is accelerated in a straight line.
C)it is carried horizontally at constant speed.
D)all of the above

Question 56

If a force on an object is aimed opposite the direction of the object's velocity,the force does

A)no work.
B)positive work.
C)negative work.
D)any of the above.

Question 57

The energy of a ball rolling up an inclined plane

A)is entirely kinetic.
B)is entirely potential.
C)is both kinetic and potential.
D)none of the above

Question 58

For a body oscillating at the end of a spring,the energy is

A)kinetic energy.
B)elastic potential energy.
C)gravitational potential energy.
D)all of the above.
E)none of the above.

Question 59

In a closed system,the kinetic energy plus the potential energy is a constant.

Question 60

Consider a situation where a skater pulls her arms inward, causing her rotation rate to speed up.
Linear momentum

A)is definitely conserved.
B)is definitely not conserved.
C)may or may not be conserved.
D)none of the above

Question 61

Consider a situation where a skater pulls her arms inward, causing her rotation rate to speed up.
Kinetic energy

A)is definitely conserved.
B)is definitely not conserved.
C)may or may not be conserved.
D)none of the above

Question 62

About how many 100-W light bulbs would you have to light up to use energy at the rate of one horsepower?

A)one or two
B)seven or eight
C)the question doesn't make sense-hp and W are unrelated
D)dozens
E)none of the above

Question 63

An object moving in a circle at a steady speed has

A)constant linear momentum.
B)constant angular momentum.
C)constant velocity.
D)constant acceleration.

Question 64

A kid slides down an icy (frictionless) hill starting from rest. At the top his gravitational potential energy is 500 J.
His kinetic energy at the top of the hill is

A)0 J.
B)500 J.
C)some value between 0 and 500 J.
D)none of the above.

Question 65

When we say work is done by a force,we mean the force does

A)all the work.
B)positive work.
C)negative work.
D)zero work.

Question 66

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t.
The quantity Fd/t is

A)the kinetic energy of the crate.
B)the potential energy of the crate.
C)the linear momentum of the crate.
D)the work you do on the crate.
E)the power you supply to the crate.

Question 67

Using a lever to move a rock reduces the force a person must exert.What does it do to the work the person must do?

A)it reduces the work also
B)the work stays the same
C)the work increases
D)none of the above

Question 68

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t.
The quantity Fd is

A)the kinetic energy of the crate.
B)the potential energy of the crate.
C)the linear momentum of the crate.
D)the work you do on the crate.
E)the power you supply to the crate.

Question 69

Consider a situation where a constant force of 25 N acts on an object having a mass of 2 kg for 3 seconds.
What is the magnitude of the change in the object's momentum?

A)150 kg m/s
B)50 kg m/s
C)75 kg m/s
D)undetermined-not enough information given
E)none of the above

Question 70

After an elastic collision of two balls,the kinetic energies of the two balls are measured to be 12 J and 24 J.What can be said about the kinetic energy of the two balls before the collision?

A)nothing-not enough information is given
B)the balls had the same energies,12 J and 24 J,respectively
C)the total kinetic energy of the two balls was 36 J
D)none of the above

Question 71

A person runs up a long flight of stairs in 10 seconds.If the person's weight is 600 N and the vertical height of the stairs is 20 meters,the person's power output is

A)0.
B)3 W.
C)30 W.
D)1,200 W.
E)12,000 W.

Question 72

Consider a situation where a constant force of 25 N acts on an object having a mass of 2 kg for 3 seconds.
What is the impulse provided by the force?

A)150 N-s
B)50 N-s
C)75 N-s
D)undetermined-not enough information given
E)none of the above

Question 73

When we say work is done against a force,we mean the force does

A)none of the work.
B)positive work.
C)negative work.
D)zero work.

Question 74

A watt is equal to

A)746 horsepower.
B)one calorie.
C)one joule.
D)1 J/s.
E)a unit of energy.

Question 75

Which of the following quantities are conserved in an isolated system?

A)mass
B)energy
C)momentum
D)all of the above

Question 76

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t.
The quantity 1/2 mv² is

A)the kinetic energy of the crate.
B)the potential energy of the crate.
C)the linear momentum of the crate.
D)the work you do on the crate.
E)the power you supply to the crate.

Question 77

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t.
The quantity mv is

A)the kinetic energy of the crate.
B)the potential energy of the crate.
C)the linear momentum of the crate.
D)the work you do on the crate.
E)the power you supply to the crate.

Question 78

A kid slides down an icy (frictionless) hill starting from rest. At the top his gravitational potential energy is 500 J.
He slides part way down the hill to a point where his gravitational potential energy is 200 J.His kinetic energy at that point will be

A)200 J.
B)300 J.
C)some unknown value between 0 and 500 J.
D)none of the above.

Question 79

A 2-kg car moving towards the right at 4 m/s collides head on with an 8 kg car moving towards the left at 2 m/s,and they stick together.After the collision,the velocity of the combined bodies is

A)0.
B)0.8 m/s towards the right.
C)0.8 m/s towards the left.
D)2.4 m/s towards the right.
E)2.4 m/s towards the left.

Question 80

Consider a situation where a constant force of 25 N acts on an object having a mass of 2 kg for 3 seconds.
What is the work done by the force?

A)150 J
B)50 J
C)75 J
D)undetermined-not enough information given
E)none of the above