A 20 kg crate initially at rest on a horizontal floor requires a 80 N horizontal force to set it in motion. Find the coefficient of static friction between the crate and the floor.

The coefficient of static friction between the crate and the floor is 0.41

Explanation:

Friction Force

When an object is moving and encounters friction in the air or rough surfaces, it loses acceleration and velocity because the friction force opposes motion.

The friction force when an object is moving on a horizontal surface is calculated by:

         [1]

Where is the coefficient of static or kinetics friction and N is the normal force.

If no forces other then the weight and the normal are acting upon the y-direction, then the weight and the normal are equal in magnitude:

N = W = m.g

The crate of m=20 Kg has a weight of:

W = 20*9.8

W = 196 N

The normal force is also N=196 N

We can find the coefficient of static friction by solving [1] for :

The friction force is equal to the minimum force required to start moving the object on the floor, thus Fr=80 N and:

The coefficient of static friction between the crate and the floor is 0.41

answer; i believe the correct answer is (40,000 j) good luck