Q: A 2 kg object moves under a net force such that its velocity changes from 3 m/s to 7 m/s. What is the net work done on the object?

$$W = \frac{1}{2} \times 2 \times (7^2$ - 3^2$) = 1 \times (49 - 9) = 40 J$$

Question 1

Which of the following best describes the law of conservation of energy as stated by Feynman?

Accepted Answer

Energy is a quantity that remains constant in a closed system, regardless of the processes occurring within.

Question 2

A block of mass $$m is $$dropped from a height $$h$$ above the ground. What is the work done by gravity as the block falls to the ground?

Accepted Answer

$$W = mgh$$

Question 3

Which of the following statements about work is correct?

Accepted Answer

Work is a scalar quantity and can be positive, negative, or zero depending on the angle between force and displacement.

Question 4

A spring with elastic constant $$k is $$stretched from $$x_1 to$$ $$x_2. $$What is the work done by the elastic force?

Accepted Answer

$$W = \frac{1}{2}k(x_1$^2 - x_2$^2)$$

Question 5

A force $$\vec{F}$$ acts on a particle causing a displacement $$d\vec{r}. $$The infinitesimal work done is given by:

Accepted Answer

$$dW = \vec{F} \cdot d\vec{r}$$

Question 6

A person lifts a barbell vertically upward at constant speed. Which force does positive work on the barbell?

Accepted Answer

The force exerted by the person

Question 7

The work done by a force is zero when:

Accepted Answer

The force is perpendicular to the displacement.

Question 8

A 2 kg object moves under a net force such that its velocity changes from 3 m/s to 7 m/s. What is the net work done on the object?

Accepted Answer

$$W = \frac{1}{2} 	imes 2 	imes (7^2$ - 3^2$) = 1 	imes (49 - 9) = 40 J$$

Question 9

Which of the following is the correct expression for the work done by a constant force $$\vec{F}$$ over a displacement $$\vec{r}_{12}$$?

Accepted Answer

$$W = \vec{F} \cdot \vec{r}_{12}$$

Question 10

A car of mass $$m$$ accelerates from rest to speed $$v on a $$flat road. Neglecting friction, what is the net work done on the car?

Accepted Answer

$$W = \frac{1}{2} m v^2$

Question 11

Which of the following is NOT a form of potential energy discussed in the materials?

Accepted Answer

Kinetic energy

Question 12

A block slides down a frictionless incline. Which principle can be used to find its speed at the bottom?

Accepted Answer

Work-energy principle

Question 13

The work-energy principle states:

Accepted Answer

The net work done on an object equals its change in kinetic energy.

Question 14

A spring (constant $$k) is $$compressed from $$x=0 to$$ $$x=a. $$What is the work done by the spring?

Accepted Answer

$$W = -\frac{1}{2} k a^2$

Question 15

Which of the following is true about the work done by gravity on a falling object?

Accepted Answer

It depends only on the initial and final heights.

Question 16

A force acts at an angle $$	heta to $$the direction of displacement. The work done is:

Accepted Answer

$$W = F d \cos 	heta$$

Question 17

A 5 kg object is pushed with a constant force of 20 N over a distance of 4 m at an angle of $$60^\circ to $$the direction of motion. What is the work done by the force?

Accepted Answer

$$W = 20 	imes 4 	imes \cos 60^\circ = 40 J$$

Question 18

Which of the following is a correct statement about the work done by friction?

Accepted Answer

It is generally negative, as friction opposes motion.

Question 19

If the net work done on a particle is zero, what can be said about its kinetic energy?

Accepted Answer

Its kinetic energy remains unchanged.

Work and Energy: Principles, Calculations, and Applications

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