The magnitude of the normal force is 35 N, the friction force is 15 N, and the net force is 70 N. What is the magnitude of the applied force? Explain your answer.

Question

The Fn and Fg force have the same sized arrows in the free-body diagram. While the Ff has a smaller arrow than the Fa in the diagram. Would the applied force be 85 N with all this information?

Answer 1

The net force is the resultant of the applied force and the frictional force, so we can write

F_net = F_applied - F_friction We subtract F_friction because friction is a retarding force.

Solving for F_applied = F_net + F_friction = 70 N + 15 N = 85 N

The normal force is balanced by the weight. The normal force is related to the friction force by

F_friction = F_normal x μ where μ is the coefficient of friction.