Why is it important to know the direction of the force applied to a moving object and the direction in which the object is moving when determining the work done on the object? a. only the component of the force perpendicular to the motion is used to calculate the work. b. if the force acts in the same direction as the motion, then no work is done. c. when there is an angle between the two directions, the cosine of the angle must be considered. d. a force at a right angle to the motion requires the use of the sine of the angle.

The correct answer is
C. When there is an angle between the two directions, the cosine of the angle must be considered.

In fact, the work done on an object by a force of magnitude F is given by

where F is the magnitude of the force, d is the distance covered and  is the angle between the force direction and the direction of motion of the object. In other words, only the component of the force parallel to the direction of motion of the object does work, this is why the cosine of the angle must be taken into account when calculating the work done.