Practice Kinetic Friction 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 friction force that opposes sliding motion between two surfaces in contact; in the simple dry-friction model its magnitude is $f_k = \mu_k N$ , directed opposite to the motion.

Once something is moving, friction resists its motion — less than static friction, but still present.

Showing a random 20 of 50 problems.

Example 1

easy

20\,\text{kg}

box slides on a level floor with

\mu_k = 0.2

and

g = 10\,\text{m/s}^2

. Find the kinetic friction force.

Example 2

hard

3\,\text{kg}

block slides up a

30^\circ

incline at

8\,\text{m/s}

with

\mu_k = 0.2

and

g = 10\,\text{m/s}^2

. How far up does it travel before momentarily stopping?

Example 3

easy

A 2 kg block slides on level ground,

\mu_k = 0.5

g = 10\,\text{m/s}^2

. Find the friction force.

Find the kinetic friction force on the 2 kg sliding block.

Example 4

hard

4\,\text{kg}

block on level ground is pushed by a

30\,\text{N}

force directed

30^\circ

below horizontal. With

\mu_k = 0.3

and

g = 10\,\text{m/s}^2

, find the acceleration.

Example 5

medium

A block slides on level ground and decelerates at

3\,\text{m/s}^2

due to friction alone. Find

\mu_k

(

g = 10\,\text{m/s}^2

Example 6

challenge

A 2 kg block is launched up a

37^\circ

incline at

10\,\text{m/s}

. With

\mu_k = 0.25

and

g = 10\,\text{m/s}^2

(

\sin 37^\circ = 0.6

\cos 37^\circ = 0.8

), how far up the incline does it travel before stopping?

Going up: both W sin37° and f_k act down the slope. Find stopping distance.

Example 7

medium

A block decelerates at

4\,\text{m/s}^2

on level ground due to friction alone (

g = 10\,\text{m/s}^2

). Find

\mu_k

Example 8

challenge

A 3 kg block on level ground is pushed with

24\,\text{N}

for

2\,\text{s}

then released. With

\mu_k = 0.2

g = 10\,\text{m/s}^2

, find the total distance until it stops.

Phase 1 (pushed): F_net

Example 9

hard

Why does dragging a

10\,\text{kg}

box at constant velocity require force only

30\,\text{N}

, less than its weight

100\,\text{N}

Example 10

medium

A block sliding with

\mu_k = 0.3

enters a level patch at

6\,\text{m/s}

and stops due to friction alone (

g = 10\,\text{m/s}^2

). How far does it travel?

Example 11

easy

A box on a horizontal surface has normal force

N = 50\,\text{N}

and

\mu_k = 0.4

. Find the kinetic friction force as it slides.

Find the kinetic friction force given N

Example 12

hard

5\,\text{kg}

block has

\mu_k = 0.4

g = 10\,\text{m/s}^2

, and is pulled by a constant horizontal

30\,\text{N}

force from rest. Find its speed after

4\,\text{m}

Example 13

hard

Two blocks of mass

2\,\text{kg}

and

3\,\text{kg}

are connected by a string on a level table,

\mu_k = 0.2

both,

g = 10\,\text{m/s}^2

. A

25\,\text{N}

force pulls the

3\,\text{kg}

block. Find the acceleration.

Example 14

easy

Kinetic friction on a sliding puck is

f_k = 6\,\text{N}

with normal force

N = 30\,\text{N}

. Find

\mu_k

Given f_k = 6 N and N = 30 N, find μ_k = f_k / N.

Example 15

challenge

2\,\text{kg}

block is launched up a

53^\circ

incline at

12\,\text{m/s}

. With

\mu_k = 0.25

and

g = 10\,\text{m/s}^2

(

\sin 53^\circ = 0.8

\cos 53^\circ = 0.6

), how far up the incline does it travel before stopping?

Example 16

medium

10\,\text{kg}

block on level ground is pushed with

40\,\text{N}

\mu_k = 0.3

g = 10\,\text{m/s}^2

. Find the net horizontal force.

Example 17

medium

3\,\text{kg}

block slides

5\,\text{m}

on level ground with

\mu_k = 0.4

g = 10\,\text{m/s}^2

. How much heat is generated?

Example 18

medium

4\,\text{kg}

block slides on level ground with

\mu_k = 0.25

and no applied force (

g = 10\,\text{m/s}^2

). Find its deceleration.

Example 19

medium

A block slides 4 m across a floor against kinetic friction

f_k = 8\,\text{N}

. How much mechanical energy is converted to heat?

Example 20

easy

50\,\text{N}

horizontal push moves a

10\,\text{kg}

box at constant velocity on a level floor. Find

\mu_k

(

g = 10\,\text{m/s}^2

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Friction Normal Force Net Force Work