Practice Work-Energy Theorem in Physics

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

The net work done on an object by all forces acting on it equals the change in its kinetic energy.

The total work done on an object is exactly what changes its kinetic energy.

Showing a random 20 of 50 problems.

Example 1

easy

The net work done on an object equals the change in its ___.

Example 2

hard

2\text{ kg}

block at

6\text{ m/s}

slides up a rough incline (

\mu_k = 0.3

, angle

25°

). Find the distance it travels before stopping (use

g = 9.8

\sin 25° \approx 0.423

\cos 25° \approx 0.906

Example 3

easy

If the net work on an object is zero, what can you conclude about its kinetic energy?

Example 4

challenge

0.2\text{ kg}

ball on a

1\text{ m}

string is released from rest at horizontal. Using the work-energy theorem, find its speed at the lowest point of the swing (use

g = 9.8

Example 5

medium

A 2 kg object at 8 m/s has -48 J of net work done on it. Find its final speed.

Example 6

easy

Does the work-energy theorem use net work or the work of a single force?

Example 7

hard

5\text{ kg}

block at

8\text{ m/s}

slides up a frictionless

30°

incline. How far along the incline does it travel before stopping (use

g = 9.8

Example 8

medium

A 2 kg block is pushed 4 m by 12 N while friction of 4 N opposes it. Find the final speed from rest.

Example 9

easy

Friction does -20 J of net work on a sliding block. What happens to its KE?

Example 10

hard

1500\text{ kg}

car traveling at

20\text{ m/s}

skids to a stop in

25\text{ m}

. Find the coefficient of kinetic friction (use

g = 9.8

Example 11

medium

1\text{ kg}

box at

10\text{ m/s}

is slowed by friction to

4\text{ m/s}

over

7\text{ m}

. Find the friction force.

Example 12

hard

0.5\text{ kg}

ball is dropped from

5\text{ m}

onto a spring, compressing it

0.1\text{ m}

before stopping. Find the average spring force (use

g = 9.8

Example 13

easy

0.5\text{ kg}

ball's kinetic energy increases from

4\text{ J}

9\text{ J}

. What net work was done?

Example 14

hard

1\text{ kg}

box is pulled by a horizontal

20\text{ N}

force across a

5\text{ m}

rough floor (

\mu_k = 0.4

). Find its final speed from rest (use

g = 9.8

Example 15

challenge

A 1200 kg car's engine and friction together do net work of 240000 J accelerating it from rest. Find the final speed.

Example 16

easy

4 \text{ kg}

box initially at rest is pushed with a net force of

20 \text{ N}

over

5 \text{ m}

. What is the final speed of the box?

Example 17

medium

3\text{ kg}

block at

4\text{ m/s}

is pushed by a net force of

6\text{ N}

over

5\text{ m}

in its direction of motion. Find its final speed.

Example 18

medium

A 5 N net force acts over 4 m on a 2 kg object from rest. Find its final speed.

Example 19

medium

A force does positive work on a moving object. Its speed must ___.

Example 20

medium

0.4\text{ kg}

arrow leaves a bow at

50\text{ m/s}

. The bowstring acts over

0.6\text{ m}

. What average net force did the string exert?

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Related Concepts

Work Kinetic Energy Power