## College Physics (4th Edition)

(a) $47,300~J$ of work must be done to raise the pile driver. (b) The work done by gravity on the pile driver is $-47,300~J$ (c) The work done by gravity on the pile driver is $47,300~J$
(a) We can find the change in gravitational potential energy: $\Delta PE = mgh$ $\Delta PE = (402~kg)(9.80~m/s^2)(12~m)$ $\Delta PE = 47,300~J$ $47,300~J$ of work must be done to raise the pile driver. (b) The change in gravitational potential energy is $47,300~J$. Therefore, the work done by gravity on the pile driver is $-47,300~J$ (c) As the pile driver falls, the change in gravitational potential energy is $-47,300~J$. Therefore, the work done by gravity on the pile driver is $47,300~J$