A particle moves a distance of 150 ft along a straight line. As it moves, it is acted upon by a constant force of magnitude 15 lb in a direction opposite to that of the motion. What is the work done by the force?
A) $-\frac{1}{2250}$ ft-lb
B) $-10$ ft-lb
C) -2250 ft-lb
D) $-\frac{1}{10}$ ft-lb

Question

Quizplus · Accepted Answer

The work done by a force is given by the dot product of the force and the displacement vector. In this case, the force is opposite to the direction of motion, so the dot product is simply the product of the magnitudes of the force and displacement, multiplied by -1 (since the force is acting in the opposite direction). Thus, the work done is:
work = -15 lb x 150 ft = -2250 ft-lb. 
Therefore, the answer is C.

A Particle Moves a Distance of 150 Ft Along a Straight