Question

1. which of the following is an example of kinetic energy?

a. a stretched rubber band
b. a book on a shelf
c. a rolling basketball
d. gasoline stored in a tank

1. potential energy is best described as:

a. energy due to motion
b. energy stored because of position or shape
c. energy lost to friction
d. energy that cannot be converted to other forms

1. a skier at the top of a hill has 20,000 j of potential energy. as the skier moves downhill,

what happens to this energy?
a. it is destroyed
b. it is converted into kinetic energy
c. it disappears as heat
d. it increases without limit

1. which of the following is an example of mechanical energy?

a. light from a lamp
b. electricity flowing in a wire
c. wind turning a windmill
d. heat from a stove

1. work is done when:

a. a force is applied but the object does not move
b. an object moves in the direction of a force
c. a force acts at a right angle to motion
d. no energy changes form

1. the power of a machine describes:

a. how much energy it can store
b. how fast work is done
c. how much force it applies
d. how much potential energy it has

1. which of the following has the most kinetic energy? (you might have to do some math)

a. a 2 kg ball rolling at 5 m/s
b. a 1 kg ball rolling at 10 m/s
c. a 3 kg ball rolling at 3 m/s
d. a 5 kg ball at rest

Explanation:

19. Kinetic Energy Identification

Kinetic energy is the energy of motion.

• A stretched rubber band has elastic potential energy.
• A book on a shelf has gravitational potential energy.
• A rolling basketball is in motion, so it has kinetic energy.
• Gasoline stored in a tank has chemical potential energy.

20. Potential Energy Definition

Potential energy is energy stored due to position or shape.

• Energy due to motion is kinetic energy.
• Energy lost to friction is dissipated as heat (not potential energy).
• All forms of energy can be converted (law of conservation of energy).

21. Energy Conversion for Skier

According to the law of conservation of energy, potential energy is converted into kinetic energy as the skier moves downhill (loses height and gains speed). Energy cannot be destroyed (a is wrong), it doesn't disappear as heat (c is wrong, unless there is significant friction which isn't indicated here), and it doesn't increase without limit (d violates conservation laws).

22. Mechanical Energy Example

Mechanical energy is the sum of kinetic and potential energy in a system.

• Light from a lamp is electromagnetic energy.
• Electricity flowing in a wire is electrical energy.
• Wind turning a windmill involves the motion (kinetic) of wind (mechanical energy).
• Heat from a stove is thermal energy.

23. Work Definition

Work is done when a force causes an object to move in the direction of the force.

• If a force is applied but no movement (a), no work.
• If force is at a right - angle to motion (c), \(W = Fd\cos\theta\) (\(\theta = 90^{\circ}\), \(\cos\theta=0\), so \(W = 0\)).
• Work is related to energy transfer (d is wrong).

24. Power Definition

Power \(P=\frac{W}{t}\), which describes how fast work is done.

• Energy storage is not power.
• Force application is not power.
• Potential energy amount is not power.

25. Kinetic Energy Calculation

The formula for kinetic energy is \(K=\frac{1}{2}mv^{2}\).

• For a: \(K_{a}=\frac{1}{2}(2)(5)^{2}=25\ J\)
• For b: \(K_{b}=\frac{1}{2}(1)(10)^{2}=50\ J\)
• For c: \(K_{c}=\frac{1}{2}(3)(3)^{2}=13.5\ J\)
• For d: \(v = 0\), so \(K_{d}=0\ J\)

Answer:

1. c. A rolling basketball
2. b. Energy stored because of position or shape
3. b. It is converted into kinetic energy
4. c. Wind turning a windmill
5. b. An object moves in the direction of a force
6. b. How fast work is done
7. b. A 1 kg ball rolling at 10 m/s