試題詳解

11. The motion of a ball of mass m dropped off a building is observed by a man at ground level and a woman at the top of the building. The man’s origin for measuring gravitational potential energy is at ground level and the woman’s origin for measuring gravitational potential energy is at the top of the building. The building’s height is h and air friction is neglected. What kinetic energy does the woman record after the ball has fallen a distance d?
(A) mgh
(B) –mgd
(C) mgd
(D) mg (h–d)