Q: A person pushes a box with a force of $$10\,\text{N}$$ over a distance of $$5\,\text{m} in $$the same direction as the force. What is the work done?

$$W = F \times d = 10 \times 5 = 50\,\text{J}$$

Q: A $$2\,\text{kg}$$ object is moving at $$3\,\text{m/s}. $$What is its kinetic energy?

$$K = \frac{1}{2} m v^2$ = \frac{1}{2} \times 2 \times 3^2$ = 9\,\text{J}$$

Q: A $$1\,\text{kg}$$ object is at a height of $$10\,\text{m}$$ above the ground. What is its gravitational potential energy relative to the ground? (Assume $$g = 9.8\,\text{m/s}^2)$$

$$PE = mgh = 1 \times 9.8 \times 10 = 98\,\text{J}$$

Q: If a machine does $$200\,\text{J} of $$work in $$4\,\text{s}$$, what is its power output?

$$P = \frac{E}{t} = \frac{200}{4} = 50\,\text{W}$$

Q: Which of the following is the correct conversion factor for horsepower to watts?

1 horsepower $$= 746\,\text{W}$$

Question 1

Which of the following best describes energy, according to the study materials?

Accepted Answer

Energy is the ability to do work and can be both a process and a thing.

Question 2

A person pushes a box with a force of $$10\,	ext{N}$$ over a distance of $$5\,	ext{m} in $$the same direction as the force. What is the work done?

Accepted Answer

$$W = F 	imes d = 10 	imes 5 = 50\,	ext{J}$$

Question 3

If the displacement of an object is opposite to the direction of the applied force, what can be said about the work done?

Accepted Answer

The work done is negative.

Question 4

What is the unit of work in the International System of Units (SI)?

Accepted Answer

Joule ($$	ext{J})$$

Question 5

Which equation correctly represents the work-energy theorem?

Accepted Answer

$$W = \Delta K = \frac{1}{2} m v_f^2$ - \frac{1}{2} m v_i^2$

Question 6

A $$2\,	ext{kg}$$ object is moving at $$3\,	ext{m/s}. $$What is its kinetic energy?

Accepted Answer

$$K = \frac{1}{2} m v^2$ = \frac{1}{2} 	imes 2 	imes 3^2$ = 9\,	ext{J}$$

Question 7

Which of the following statements about kinetic energy is correct?

Accepted Answer

Kinetic energy is proportional to the square of the speed.

Question 8

What is the main difference between kinetic energy and potential energy?

Accepted Answer

Kinetic energy is energy in motion, while potential energy is stored energy.

Question 9

A $$1\,	ext{kg}$$ object is at a height of $$10\,	ext{m}$$ above the ground. What is its gravitational potential energy relative to the ground? (Assume $$g = 9.8\,	ext{m/s}^2)$$

Accepted Answer

$$PE = mgh = 1 	imes 9.8 	imes 10 = 98\,	ext{J}$$

Question 10

Which property is key for potential energy in a system involving an object and the Earth?

Accepted Answer

Position

Question 11

What is the formula for power in terms of energy and time?

Accepted Answer

$$P = \frac{E}{t}$$

Question 12

If a machine does $$200\,	ext{J} of $$work in $$4\,	ext{s}$$, what is its power output?

Accepted Answer

$$P = \frac{E}{t} = \frac{200}{4} = 50\,	ext{W}$$

Question 13

Which of the following is the correct conversion factor for horsepower to watts?

Accepted Answer

1 horsepower $$= 746\,	ext{W}$$

Question 14

Which equation represents the conservation of mechanical energy in a system?

Accepted Answer

$$E_i = E_f ($$where $$E = K + PE)$$

Question 15

A $$1\,	ext{kg}$$ ball is dropped from a height of $$5\,	ext{m}. $$What is its speed just before hitting the ground? (Assume $$g = 9.8\,	ext{m/s}^2$$ and ignore air resistance)

Accepted Answer

$$v = \sqrt{2gh} = \sqrt{2 	imes 9.8 	imes 5} \approx 9.9\,	ext{m/s}$$

Question 16

A car accelerates from rest to $$20\,	ext{m/s}$$, and its mass is $$1000\,	ext{kg}. $$What is the change in kinetic energy?

Accepted Answer

$$\Delta K = \frac{1}{2} m v^2$ = \frac{1}{2} 	imes 1000 	imes 20^2$ = 200,000\,	ext{J}$$

Question 17

Which scenario best illustrates the transfer of energy as work?

Accepted Answer

A person lifts a box from the floor to a shelf.

Question 18

If a $$2\,	ext{kg}$$ object moves at $$4\,	ext{m/s}$$ and then slows to $$2\,	ext{m/s}$$, what is the work done by friction?

Accepted Answer

$$W = \Delta K = \frac{1}{2} 	imes 2 	imes (2^2$ - 4^2$) = \frac{1}{2} 	imes 2 	imes (-12) = -12\,	ext{J}$$

Question 19

A $$60\,	ext{kg}$$ person climbs a $$3\,	ext{m}$$ ladder in $$6\,	ext{s}. $$What is the average power output? (Assume $$g = 9.8\,	ext{m/s}^2)$$

Accepted Answer

$$P = \frac{E}{t} = \frac{mgh}{t} = \frac{60 	imes 9.8 	imes 3}{6} = 294\,	ext{W}$$

Study Notes: Energy, Work, and Power (Physics Ch. 7)

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