Question

While moving a 71 kg box across a horizontal floor, you find that it takes a 190 N force to get the box moving (pushing horizontally), but just a 120 N force to keep it moving at constant speed thereafter. What is the coefficient of static friction between box and floor? What is the coefficient of kinetic friction between box and floor?

Answer 1

Answer:

μs=  0.273

μk=  0.172

Explanation:

The formula to calculate friction force is :

f = μ *N

Where:

μ :  friction coefficient

N: Normal Force

N=W  

W = m*g= 71 kg * 9.8 m/s² = 695.8 N :  weight of the box

Problem development

fs = μs*N

μs: coefficient of static friction

fs= 190 N : Static friction force

N = 695.8 N

μs= fs / N

μs=  190 N / 695.8 N

μs=  0.273

fk = μk*N

μk: coefficient of kinetic friction between box and floor

fk= 120 N :kinetic friction force

N = 695.8 N

μk= fk / N

μk= 120 N / 695.8 N

μk=  0.172