A woman runs up a flight of stairs. The gain in her gravitational potential energy is U. If she runs up the same stairs with twice the speed, what is her gain in potential energy?

U

Explanation:

The change in gravitational potential energy only depends of the difference in height (in this case the number of stairs), so as the height remained the same, her gain in potential energy remained the same, independent from her climbing speed.

A., d., and f i think