Practice 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

A contact force that opposes the relative motion or tendency of motion between two surfaces in contact.

The resistance you feel when sliding something across a rough surface — it always acts opposite to motion.

Showing a random 20 of 50 problems.

Example 1

easy
In which direction does kinetic friction act?

Example 2

hard
A 50 kg50 \text{ kg} crate is pushed up a 30∘30^\circ incline at constant speed by a force parallel to the slope. μk=0.2\mu_k = 0.2, g=10 m/s2g = 10 \text{ m/s}^2. Find the applied force.

Example 3

medium
The coefficient of static friction between a box and the floor is μs=0.4\mu_s = 0.4. If the box weighs 98 N98 \text{ N}, what is the maximum static friction force?

Example 4

medium
A 2 kg2 \text{ kg} block slides at 10 m/s10 \text{ m/s} on a floor; μk=0.5\mu_k = 0.5 (g=10 m/s2g = 10 \text{ m/s}^2). How far does it travel before stopping?

Example 5

challenge
A 4 kg4\text{ kg} block on a 37∘37^\circ incline (g=10g=10, sin⁡37∘=0.6\sin 37^\circ=0.6, cos⁡37∘=0.8\cos 37^\circ=0.8, μk=0.25\mu_k=0.25) slides down. Find its acceleration.

Example 6

easy
A 4 kg4 \text{ kg} block slides on a floor with μk=0.25\mu_k = 0.25 (g=10 m/s2g = 10 \text{ m/s}^2). Find the friction force on it.

Example 7

hard
A 15 kg15 \text{ kg} block on a surface (μk=0.25\mu_k = 0.25) is pushed with 80 N80 \text{ N}. What is the acceleration?

Example 8

medium
A 6 kg6 \text{ kg} block is pushed with a horizontal force FF and starts to slide when FF exceeds 24 N24 \text{ N}. Find μs\mu_s. Use g=10 m/s2g = 10 \text{ m/s}^2.

Example 9

medium
A block on a 30∘30^\circ incline (g=10 m/s2g = 10 \text{ m/s}^2) needs μs≥tan⁡30∘\mu_s \ge \tan 30^\circ to remain stationary. Find μs\mu_s.

Example 10

hard
A car traveling at 20 m/s20 \text{ m/s} skids to a stop in 40 m40 \text{ m}. Find μk\mu_k between tires and road. Use g=10 m/s2g = 10 \text{ m/s}^2.

Example 11

medium
A hockey puck slides 45 m45\text{ m} before stopping from 30 m/s30\text{ m/s} (g=10g=10). Find μk\mu_k (use v2=2adv^2=2ad).

Example 12

easy
Does friction depend on the contact area for solid surfaces (standard model)?

Example 13

medium
Why does friction not depend on whether you stack a book flat or on its edge (same book, same floor)?

Example 14

hard
A 2 kg2 \text{ kg} block sits on a 3 kg3 \text{ kg} board on a frictionless floor. The coefficient of static friction between block and board is 0.30.3. What's the maximum acceleration the system can have without the block slipping? Use g=10 m/s2g = 10 \text{ m/s}^2.

Example 15

medium
A 5 kg5 \text{ kg} block is pushed with 30 N30 \text{ N} horizontally; μk=0.4\mu_k = 0.4 (g=10 m/s2g = 10 \text{ m/s}^2). Find its acceleration.

Example 16

medium
A 20 kg20\text{ kg} crate (g=10g=10) needs 80 N80\text{ N} to start sliding. Find the coefficient of static friction.

Example 17

medium
A 1 kg1 \text{ kg} block slides on a horizontal floor and decelerates at 4 m/s24 \text{ m/s}^2. Find μk\mu_k (g=10 m/s2g = 10 \text{ m/s}^2).

Example 18

hard
A car rounds a banked curve of radius 50 m50 \text{ m} at 20 m/s20 \text{ m/s} on an icy (frictionless) road. What banking angle is required? Use g=10 m/s2g = 10 \text{ m/s}^2.

Example 19

hard
A 10 kg10 \text{ kg} box is on a 20∘20^\circ incline. The coefficient of static friction is μs=0.5\mu_s = 0.5. Will it slide? Use g=10 m/s2g = 10 \text{ m/s}^2.

Example 20

easy
A box needs 25 N25\text{ N} to start sliding and only 18 N18\text{ N} to keep moving. Which value is kinetic friction?
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