5. Work and energy

Question 1

The work done on an object is directly proportional to what?

Answer 1

The force on an object, its displacement, and the cosine of their angle.

Question 2

What is energy?

Answer 2

The ability to do work.

Question 3

Is work a scalar quanity?

Answer 3

Yes.

Question 4

When is work equal to zero?

Answer 4

When the force is perpendicular to an object’s displacement or when it isn’t displaced.

Question 5

What is kinetic energy?

Answer 5

The amount of energy an object has by being in motion.

Question 6

Kinetic energy, KE, is directly proportional to mass and the square of what?

Answer 6

Velocity.

Question 7

What is the work-energy principle?

Answer 7

The net work, W, done on an object is equal to the change in kinetic energy of the object.

Question 8

Total energy before and after any process is always what?

Answer 8

Equal.

Question 9

What are the two types of potential energy?

Answer 9

Gravitational and elastic.

Question 10

What is potential energy?

Answer 10

The energy stored in an object based on its position.

Question 11

Gravitational potential energy is directly related to what?

Answer 11

Mass, acceleration due to gravity, and height above the zero point.

Question 12

Elastic potential energy is directly proportional to what?

Answer 12

Spring constant and displacement of spring from equilibrium squared.

Question 13

What does the conservation of energy principle say?

Answer 13

Energy cannot be created or destroyed, only transferred.

Question 14

What happens to total mechanical energy in a closed system?

Answer 14

It stays the same.

Question 15

What is the unit of power?

Answer 15

Watt.

Question 16

What is a watt?

Answer 16

One joule of work done per second.

Question 17

Power is directly proportional to what?

Answer 17

Energy transferred.

Question 18

Total mechanical energy of a pendulum does what?

Answer 18

Stays the same.

Question 19

As a pendulum swings back and forth, the total energy stays the same, but it does transfer between what?

Answer 19

Gravitational potential energy and kinetic energy.

Question 20

In a pendulum swing, when is gravitational potential energy at its highest, and when is kinetic energy at its highest?

Answer 20

Gravitational potential energy is at its highest when it is at the highest point of the swing, and kinetic energy is at its highest at the lowest part of the swing.

Question 21

Which of the following is NOT an example of kinetic energy being converted to potential energy?

• a basketball player jumping for a rebound
• releasing a compressed spring
• squeezing a rubber ball
• pulling a sled up a hill

Answer 21

Releasing a compressed spring

Question 22

Which one is doing the most work?

• pulling a box 10 m with a force of 100 N
• pushing a box 100 m with a force of 200N
• pulling a sled 1000 m with a force of 10N
• pushing a car with a force of 100000 N and it doesn’t move

Answer 22

Pushing a box 100 m with a force of 200N

Question 23

A 100-kg rock is 100 m above the ground, what is the potential energy of the rock?

Answer 23

98000 J

Question 24

An example of potential energy is

• a basketball sitting on a rack.
• a bird flying.
• Grandma rocking in her chair.
• none of the above.

Answer 24

A basketball sitting on a rack.

Question 25

A car or truck moving down the highway has what type of energy by virtue of its motion?

Answer 25

Kinetic.

Question 26

Ethan carried a 200 Newton bag 3 meters up a ladder in 30 seconds. How much power did he use?

Answer 26

20 Watts.

Question 27

Which situation is an example of increasing potential energy? * a bicyclist stopping at a stop sign * a cat jumping from a tree * emptying a bucket of water * pulling a wagon uphill

Answer 27

Pulling a wagon uphill.

Question 28

An arrow in a bow has 70 J of potential energy. Assuming no loss of energy due to heat, how much kinetic energy will it have after it has been shot?

Answer 28

70 J

Question 29

Imagine an object held at some height above the ground. It is released and falls toward the ground. Ignoring air resistance or friction, which of the following must be true? * Before it falls, all of its energy must be potential energy. * At the end of its fall, all of its energy must be converted to kinetic energy. * During its fall, the combination of its kinetic and potential energy must equal the amount of potential energy with which it started. * All of the above are true

Answer 29

All of the above are true

Question 30

An object with the mass of .1 kg was dropped from a cliff 200 m high. Immediately before hitting the ground, it was clocked to travel with the speed of 40 m/s. Calculate how much energy was dissipated by the air drag.

Answer 30

120 J