A 200 N box is pushed at a constant velocity up an incline that is 5.00 m long and rises 1 m. If the incline is frictionless, then the work done by the pushing force is
A) 336 J.
B) 305 J.
C) 275 J.
D) 200 J.
E) 157 J.

Question

Quizplus · Accepted Answer

Since the box is moving at a constant velocity, the net force on the box must be zero. This means that the force of gravity (weight) pulling the box down the incline is exactly offset by the force pushing the box up the incline. The work done by the pushing force is given by the distance it moves the box, multiplied by the component of the pushing force that is parallel to the incline. In this case, the pushing force is exactly equal and opposite to the weight of the box, so the magnitude of the parallel component of the pushing force is just the weight of the box times the sine of the angle of the incline (which is 1/5). Thus, the work done by the pushing force is:

W = F_parallel * d = (200 N) * sin(1/5) * 5.00 m = 200 J

Therefore, the answer is D) 200 J.

A 200 N Box Is Pushed at a Constant Velocity