Question

A mover carries a 15-kg box for 20 m. How much work did he do?

Answer 1

Actually he did no work at all! when picking up the box he did work against gravity. When setting it down gravity did the same work back to the mover. (Gravity is a conservative force so the path of the box is immaterial). While walking with the box the displacement is perpendicular to the force so the dot product is zero there.

Answer 2

W= F·d
W=
`F_g`·d
W=mg·d
W=(15x9.8)20
W= 2,940 J (Joules)

2,940 joules of work was done