Question

A box has mass 13 kg and is at rest on a flat floor. A minimum force of 47 N is needed to push the box so it moves across the floor. What is the coefficient of static friction between the box and floor?

Answer 1

let's call
 N=Normal force.
 m*g=Weight.
 F= Force needed to move the block.
 f = friction force.
 k = static friction coefficient.
 For balance:
 N = mg and F = f
 By definition
 f=k*N.
 Clearing this last expression:
 k=f/N.
 Substituting:
 k=f/N=F/m*g=(47)/((13)*(9.8))=0.37
 the coefficient of static friction between the box and floor is 0.37