Which of the following is NOT an example of work?

a. a windmill turning in the wind

b. a person sliding a box across the floor

c. a metal bar bracing a leaning brick wall

d. an air bag deploying in an automobile wreck

Work = (force) · (distance)

a). The wind does work on the windmill.

b). The person does work on the box.

c). The metal bar exerts force on the leaning wall,

but nothing moves, so there's no work done.

d). The explosive inflator does work on the airbag, and very soon

after that, the driver and passengers do work on it too.