Question

7. A box is pulled straight across the floor at a constant speed. It is pulled with a horizontal force of 48 N.
a. Find the net force (in N) on the box.
b. Find the force of friction (in N) from the floor on the box.
c. The person pulling on the box stops pulling and the box comes to a rest. Find the force of friction (in N) on the box when at rest.

Answer 1

a) The Newton’s second law states

F_net=ma

The box is pulled at constant speed, so it acceleration is zero. Therefore F_net=0.

b) The net force

F_net=F-F_frict

So

F_frict=F=48 N

c) When the box on the horizontal floor is at rest, the friction force is zero.