Question

A gust of wind blowing east pushes against a ball. When will the wind do work on the ball?

Answer 1

As soon as the ball moves, the force of the wind
has been applied through some distance.

That's when work is done, because Work = (force) x (distance) .

Answer 2

Answer: when the ball moves in the same direction in which the wing blows (to the east).

Step-by-step explanation:

Work is done when a force causes motion of an object along the same direction as the force acts.

For example, if a person holds up a heavy bowling ball but such person translates the ball horizontally, the motion and the force are perpendicular meaning that person is not doing any work on the ball.

On the other hand, if the person pushes or pulls the ball with a force parallel to the ground (motion), now wor is done:

W = Force × displacement × cos (angle between the force and the displacement)

If the angle is 90°, cos (90°) = 0 ⇒ W = 0.