Question

in which situations is work being done?
hannah leans against her locker, but it doesnt move.
andys car rolls down a hill with the engine off.
a wind turbine stands still on a sunny, windless day.
a balloon expands as it is heated by the sun.
james pedals a stationary exercise cycle that doesnt move.

Explanation:

Work is done when a force causes an object to move in the direction of the force. In the case of Hannah leaning against the locker, no movement occurs despite the force applied, so no work is done. For the wind - turbine standing still, there is no force causing movement. When James pedals a stationary exercise cycle that doesn't move, although force is applied, there is no displacement in the direction of the force. Andy's car rolling down a hill has a force (gravity) causing it to move, and a balloon expanding as it is heated by the Sun has a force (pressure from heated gas) causing a change in volume (displacement in a sense).

Answer:

B. Andy's car rolls down a hill with the engine off; D. A balloon expands as it is heated by the Sun