A boy pulls a load with a rope inclined at $60^\circ$ to the horizontal using a force of $100$ N. If the load moves $5$ m horizontally, find the work done.

Only the horizontal component of the force does work along the displacement: $W = Fd\cos\theta = 100 \times 5 \times \cos 60^\circ = 500 \times 0.5 = 250$ J. Using $\sin 60^\circ$ gives 433 J, and ignoring the angle gives 500 J.