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.

a) Taking into consideration Newton's second law, we know that

Net_Force = mass * acceleration

Since the box is pulled at constant speed, the acceleration is equal to zero.

This means that

Net_Force = 0 N

b) Force of friction

The net force is equal to the sum of all forces,

Net_Force = Force_applied - Friction

We found that Net_Force = 0, which means

Friction = Force_applied = 48 N

c) If the box comes to a stop. And the applied force becomes zero, the friction force becomes also zero.

Friction = 0 N