Question

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

when the ball moves to the east
when the ball moves to the north
when the ball stays in one place
when the ball moves north or south

Answer 1

Work is W = F · s. The wind force is eastward, so it does work only when the ball has an eastward displacement (cosθ ≠ 0).

Thus: the wind does work when the ball moves to the east (or any motion with an eastward component). If the ball moves purely north/south or stays in place, the work is zero. If it moves west, the wind does negative work.