Q: A box is pushed with a force of $$10\ \mathrm{N}$$ over a displacement of $$5\ \mathrm{m} in $$the same direction as the force. What is the work done on the box?

$$W = Fd = 10 \times 5 = 50\ \mathrm{J}$$

Q: A person lifts a $$2\ \mathrm{kg}$$ object to a height of $$3\ \mathrm{m}. $$What is the increase in gravitational potential energy? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

$$\Delta PE = mgh = 2 \times 9.8 \times 3 = 58.8\ \mathrm{J}$$

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

$$v = \sqrt{2gh} = \sqrt{2 \times 9.8 \times 5} = 9.9\ \mathrm{m/s}$$

Question 1

Which of the following best describes the concept of energy as outlined in the study materials?

Accepted Answer

Energy is the ability to do work.

Question 2

A box is pushed with a force of $$10\ \mathrm{N}$$ over a displacement of $$5\ \mathrm{m} in $$the same direction as the force. What is the work done on the box?

Accepted Answer

$$W = Fd = 10 	imes 5 = 50\ \mathrm{J}$$

Question 3

Which of the following statements about work is correct?

Accepted Answer

Work can be positive or negative depending on the direction of force and displacement.

Question 4

If a force acts at an angle $$	heta to $$the direction of displacement, which formula correctly calculates the work done?

Accepted Answer

$$W = Fd\cos	heta$$

Question 5

What are the SI units of work?

Accepted Answer

Joules ($$\mathrm{J})$$

Question 6

A person lifts a $$2\ \mathrm{kg}$$ object to a height of $$3\ \mathrm{m}. $$What is the increase in gravitational potential energy? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$\Delta PE = mgh = 2 	imes 9.8 	imes 3 = 58.8\ \mathrm{J}$$

Question 7

Which of the following best describes kinetic energy?

Accepted Answer

The energy of an object due to its motion.

Question 8

According to the work-energy theorem, what is the relationship between net work and kinetic energy?

Accepted Answer

$$W_{net} = \Delta K = \frac{1}{2}mv_f^2$ - \frac{1}{2}mv_i^2$

Question 9

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

Accepted Answer

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

Question 10

Which of the following is a correct statement about potential energy?

Accepted Answer

Potential energy is stored energy due to position.

Question 11

A car engine does $$15,000\ \mathrm{J} of $$work in $$10\ \mathrm{s}. $$What is the average power output?

Accepted Answer

$$P = \frac{E}{t} = \frac{15,000}{10} = 1,500\ \mathrm{W}$$

Question 12

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

Accepted Answer

$$1\ \mathrm{hp} = 746\ \mathrm{W}$$

Question 13

Which equation represents the conservation of mechanical energy for an object in free fall?

Accepted Answer

$$\frac{1}{2}mv_i^2$ + mgh_i = \frac{1}{2}mv_f^2$ + mgh_f$$

Question 14

A $$60\ \mathrm{kg}$$ person runs up a $$5\ \mathrm{m}$$ high flight of stairs in $$4\ \mathrm{s}. $$What is their average power output? ($$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$P = \frac{mgh}{t} = \frac{60 	imes 9.8 	imes 5}{4} = 735\ \mathrm{W}$$

Question 15

If the work done by friction on a sliding object is $$-20\ \mathrm{J}$$, what does the negative sign indicate?

Accepted Answer

The force of friction acts opposite to the direction of displacement.

Question 16

Which of the following scenarios best illustrates the transfer of energy as work?

Accepted Answer

A person pushes a stalled car, causing it to move.

Question 17

Which of the following is NOT a property of potential energy?

Accepted Answer

It is always associated with motion.

Question 18

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

Accepted Answer

$$K = \frac{1}{2}mv^2$ = \frac{1}{2} 	imes 2 	imes 3^2$ = 9\ \mathrm{J}$$

Question 19

Which of the following best describes the relationship between kinetic energy and speed?

Accepted Answer

Kinetic energy is proportional to the square of the speed.

Chapter 7: Energy, Work, and Power – Study Notes

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