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 kg crate is pushed up a 30∘ incline at constant speed by a force parallel to the slope. μk=0.2, g=10 m/s2. Find the applied force.
Example 3
medium
The coefficient of static friction between a box and the floor is μs=0.4. If the box weighs 98 N, what is the maximum static friction force?
Example 4
medium
A 2 kg block slides at 10 m/s on a floor; μk=0.5 (g=10 m/s2). How far does it travel before stopping?
Example 5
challenge
A 4 kg block on a 37∘ incline (g=10, sin37∘=0.6, cos37∘=0.8, μk=0.25) slides down. Find its acceleration.
Example 6
easy
A 4 kg block slides on a floor with μk=0.25 (g=10 m/s2). Find the friction force on it.
Example 7
hard
A 15 kg block on a surface (μk=0.25) is pushed with 80 N. What is the acceleration?
Example 8
medium
A 6 kg block is pushed with a horizontal force F and starts to slide when F exceeds 24 N. Find μs. Use g=10 m/s2.
Example 9
medium
A block on a 30∘ incline (g=10 m/s2) needs μs≥tan30∘ to remain stationary. Find μs.
Example 10
hard
A car traveling at 20 m/s skids to a stop in 40 m. Find μk between tires and road. Use g=10 m/s2.
Example 11
medium
A hockey puck slides 45 m before stopping from 30 m/s (g=10). Find μk (use v2=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 kg block sits on a 3 kg board on a frictionless floor. The coefficient of static friction between block and board is 0.3. What's the maximum acceleration the system can have without the block slipping? Use g=10 m/s2.
Example 15
medium
A 5 kg block is pushed with 30 N horizontally; μk=0.4 (g=10 m/s2). Find its acceleration.
Example 16
medium
A 20 kg crate (g=10) needs 80 N to start sliding. Find the coefficient of static friction.
Example 17
medium
A 1 kg block slides on a horizontal floor and decelerates at 4 m/s2. Find μk (g=10 m/s2).
Example 18
hard
A car rounds a banked curve of radius 50 m at 20 m/s on an icy (frictionless) road. What banking angle is required? Use g=10 m/s2.
Example 19
hard
A 10 kg box is on a 20∘ incline. The coefficient of static friction is μs=0.5. Will it slide? Use g=10 m/s2.
Example 20
easy
A box needs 25 N to start sliding and only 18 N to keep moving. Which value is kinetic friction?