A box of mass 22 kg is at rest on a flat floor. The coefficient of static friction between the box and floor is 0.37. What is the minimum force needed to set the box in motion across the floor?

112 N
80 N
56 N
216 N

Question

A box of mass 22 kg is at rest on a flat floor. The coefficient of static friction between the box and floor is 0.37. What is the minimum force needed to set the box in motion across the floor?
 	
	112 N
	80 N
	56 N
	216 N

matt101 · Answer

The minimum force needed to set the box in motion is the force needed to overcome static friction. If you find the force of static friction, you find your minimum force. The equation for the frictional force is:

$$f= \mu_sF_N$$
Where f is the force of friction, μ(s) is the coefficient of static friction, and F(N) is the normal force. Remember, the normal force on the object is (in many cases, including this one), equal to mg.

What do you get?