A horizontal force of 12 Newtons is applied to a 4.0 kg box that slides on a horizontal surface.The box starts from rest moves a horizontal distance of 10 meters and obtains a velocity of 5.0 m/s.The surface has friction.The friction force is
A) 7.0 N.
B) 6.5 N.
C) 6.0 N.
D) 5.7 N.
E) 4.9 N.

Question

Quizplus · Accepted Answer

The correct answer is A because the friction force is equal to the difference between the applied force and the force required to accelerate the box. The force required to accelerate the box is equal to the mass of the box times its acceleration. The acceleration of the box is equal to the change in velocity divided by the time it takes to make the change. The time it takes to make the change is equal to the distance traveled divided by the velocity. Therefore, the friction force is equal to:$$F_f = F_a - ma = ma - ma = 0$$

A Horizontal Force of 12 Newtons Is Applied to a 4.0