Q: A force $$\vec{F}$$ acts at an angle $$\theta to $$the displacement $$\vec{s}. $$Which formula gives the work done by this force?

$$W = F \cdot s \cdot \cos \theta$$

Q: A box of mass $$m is $$pushed from $$x_1 to$$ $$x_2 by a $$net force $$\vec{F}$$, increasing its speed from $$v_1 to$$ $$v_2. $$According to the work-energy theorem, which equation is correct?

$$W_{\text{net}} = \frac{1}{2} m v_2$^2 - \frac{1}{2} m v_1$^2$$

Q: A 2 kg object moves at 3 m/s. What is its kinetic energy?

$$KE = 0.5 \times 2 \times 3^2$ = 9 \ \text{J}$$

Q: A person pushes a box across a floor with a force of 50 N at an angle of 60° to the horizontal for a distance of 4 m. What is the work done by the force?

$$W = 50 \times 4 \times \cos 60^\circ = 100 \ \text{J}$$

Question 1

A baseball pitcher throws a ball, giving it kinetic energy. Which of the following best describes the work done by the pitcher on the ball?

Accepted Answer

The pitcher does work because he applies a force over a displacement, increasing the ball's kinetic energy.

Question 2

Three people push a car stuck in snow, causing it to move. Which equation correctly represents the work done by the combined force if the force and displacement are in the same direction?

Accepted Answer

$$W = F \cdot s$$

Question 3

A force $$\vec{F}$$ acts at an angle $$	heta to $$the displacement $$\vec{s}. $$Which formula gives the work done by this force?

Accepted Answer

$$W = F \cdot s \cdot \cos 	heta$$

Question 4

Which of the following scenarios results in zero work being done by a force?

Accepted Answer

A force acts perpendicular to the direction of displacement.

Question 5

A weightlifter holds a barbell stationary above his head. What is the work done by the weightlifter on the barbell?

Accepted Answer

Zero work, because there is no displacement.

Question 6

A box of mass $$m is $$pushed from $$x_1 to$$ $$x_2 by a $$net force $$\vec{F}$$, increasing its speed from $$v_1 to$$ $$v_2. $$According to the work-energy theorem, which equation is correct?

Accepted Answer

$$W_{	ext{net}} = \frac{1}{2} m v_2$^2 - \frac{1}{2} m v_1$^2$$

Question 7

Which of the following statements about kinetic energy is correct?

Accepted Answer

Kinetic energy is always zero if the object is at rest.

Question 8

A spring with force constant $$k is $$stretched by a distance $$X. $$What is the work done on the spring?

Accepted Answer

$$W = \frac{1}{2} k X^2$

Question 9

A force varies with position as a particle moves from $$x_1 to$$ $$x_2. $$How is the total work done by the force calculated?

Accepted Answer

$$W = \int_{x_1$}^{x_2$} F_x \, dx$$

Question 10

A car engine delivers a constant force $$\vec{F} to $$move a car at velocity $$\vec{v}. $$What is the instantaneous power delivered by the engine?

Accepted Answer

$$p = F \cdot v$$

Question 11

A person lifts a 10 kg box vertically upward 2 meters in 4 seconds. What is the average power output? (Take $$g = 9.8 \ 	ext{m/s}^2)$$

Accepted Answer

$$P = 19.6 \ 	ext{W}$$

Question 12

Which of the following best describes the area under a force vs. position graph?

Accepted Answer

It represents the work done by the force.

Question 13

A force acts on a particle moving along a curved path. The infinitesimal work done $$dW is $$given by:

Accepted Answer

$$dW = F \cos \phi \ dl$$

Question 14

A 2 kg object moves at 3 m/s. What is its kinetic energy?

Accepted Answer

$$KE = 0.5 	imes 2 	imes 3^2$ = 9 \ 	ext{J}$$

Question 15

A person pushes a box across a floor with a force of 50 N at an angle of 60° to the horizontal for a distance of 4 m. What is the work done by the force?

Accepted Answer

$$W = 50 	imes 4 	imes \cos 60^\circ = 100 \ 	ext{J}$$

Question 16

Which of the following is true about the SI unit of power?

Accepted Answer

It is the watt (W), where $$1 \ 	ext{W} = 1 \ 	ext{J/s}.$$

Question 17

A force does negative work on an object. What happens to the object's kinetic energy?

Accepted Answer

It decreases.

Question 18

A 1,000 kg car accelerates from rest to 20 m/s. What is the total work done on the car?

Accepted Answer

$$W = 0.5 	imes 1,000 	imes 20^2$ = 200,000 \ 	ext{J}$$

Question 19

Which of the following is a correct statement of the work-energy theorem?

Accepted Answer

The work done by the net force equals the change in the object's kinetic energy.

Work and Kinetic Energy: Concepts, Calculations, and Applications

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