Q: A person pushes a stalled car with a constant force of 400 N for a distance of 15 m in the direction of the force. How much work does the person do on the car?

$$W = 400 \times 15 = 6000\ \mathrm{J}$$

Q: A 2 kg ball is thrown with a speed of 10 m/s. What is its kinetic energy?

$$K = \frac{1}{2} m v^2$ = \frac{1}{2} \times 2 \times 10^2$ = 100\ \mathrm{J}$$

Q: A 1,200 kg car accelerates from 5 m/s to 15 m/s. What is the change in its kinetic energy?

$$\Delta K = \frac{1}{2} m (v_f^2$ - v_i^2$) = \frac{1}{2} \times 1200 \times (15^2$ - 5^2$) = 108,000\ \mathrm{J}$$

Q: A cyclist exerts a force of 200 N at an angle of $$60^\circ to $$the direction of motion over a distance of 100 m. What is the work done by the cyclist?

$$W = 200 \times 100 \times \cos 60^\circ = 10,000\ \mathrm{J}$$

Q: A box is lifted 2 m vertically at constant speed. The box has a mass of 10 kg. What is the average power output if the lift takes 4 seconds? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

$$P = \frac{m g h}{t} = \frac{10 \times 9.8 \times 2}{4} = 49\ \mathrm{W}$$

Question 1

A person pushes a stalled car with a constant force of 400 N for a distance of 15 m in the direction of the force. How much work does the person do on the car?

Accepted Answer

$$W = 400 	imes 15 = 6000\ \mathrm{J}$$

Question 2

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

Accepted Answer

A person holds a heavy box stationary above their head.

Question 3

A force of magnitude $$F$$ acts at an angle $$	heta to $$the direction of displacement $$\vec{s}. $$What is the formula for the work done by this force?

Accepted Answer

$$W = F s \cos 	heta$$

Question 4

A 2 kg ball is thrown with a speed of 10 m/s. What is its kinetic energy?

Accepted Answer

$$K = \frac{1}{2} m v^2$ = \frac{1}{2} 	imes 2 	imes 10^2$ = 100\ \mathrm{J}$$

Question 5

If the net work done on a particle is negative, what happens to its kinetic energy?

Accepted Answer

Its kinetic energy decreases.

Question 6

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

Accepted Answer

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

Question 7

A 1,200 kg car accelerates from 5 m/s to 15 m/s. What is the change in its kinetic energy?

Accepted Answer

$$\Delta K = \frac{1}{2} m (v_f^2$ - v_i^2$) = \frac{1}{2} 	imes 1200 	imes (15^2$ - 5^2$) = 108,000\ \mathrm{J}$$

Question 8

Which of the following best describes the work-energy theorem?

Accepted Answer

The net work done on a particle equals the change in its kinetic energy.

Question 9

A force $$F(x)$$ varies with position $$x. $$What is the general expression for the work done by this force as the object moves from $$x_i to$$ $$x_f$$?

Accepted Answer

$$W = \int_{x_i}^{x_f} F(x)\,dx$$

Question 10

A weightlifter lowers a barbell to the floor. Which statement is true about the work done?

Accepted Answer

The weightlifter's hands do negative work on the barbell.

Question 11

A cyclist exerts a force of 200 N at an angle of $$60^\circ to $$the direction of motion over a distance of 100 m. What is the work done by the cyclist?

Accepted Answer

$$W = 200 	imes 100 	imes \cos 60^\circ = 10,000\ \mathrm{J}$$

Question 12

Which of the following is the SI unit of power?

Accepted Answer

Watt ($$1\ \mathrm{W} = 1\ \mathrm{J}/\mathrm{s})$$

Question 13

A box is lifted 2 m vertically at constant speed. The box has a mass of 10 kg. What is the average power output if the lift takes 4 seconds? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$P = \frac{m g h}{t} = \frac{10 	imes 9.8 	imes 2}{4} = 49\ \mathrm{W}$$

Question 14

Which statement about kinetic energy is correct?

Accepted Answer

Kinetic energy depends on mass and the square of speed.

Question 15

A machine does 500 J of work in 2 seconds. What is its average power output?

Accepted Answer

$$P = \frac{500}{2} = 250\ \mathrm{W}$$

Question 16

A force acts perpendicular to the displacement of an object. What is the work done by this force?

Accepted Answer

Zero

Question 17

A 5 kg object moves in a straight line under a constant force. Its speed increases from 2 m/s to 6 m/s. What is the net work done on the object?

Accepted Answer

$$W = \Delta K = \frac{1}{2} 	imes 5 	imes (6^2$ - 2^2$) = 80\ \mathrm{J}$$

Question 18

Which of the following is true about the area under a force vs. position graph?

Accepted Answer

It represents the work done by the force over the displacement.

Chapter 06

Guida di studio - Domande di pratica

Study guide - Flashcard