Question

A box is pulled upon a rough inclined plane by an applied force Fa parallel to the plane. Which force does not do work on the box while being pulled up the inclined plane? *

A. Friction

B. Gravitational force

C. Applied force

D. Normal force

Answer 1

Here $N$ is the normal force, $F_{fr}$ is frictional force, $F$ applied force, $mg$ gravitational force. As one can see in the figure, normal force is the only force that is perpendicular to the displacement along the inclined plane. Thus, its work is zero.

Answer. D. Normal force.