## College Physics (4th Edition)

(a) $18.4~J$ of work must be done on the carton. (b) The work done by gravity on the cat litter is $8.82~J$
(a) We can find the change in gravitational potential energy: $\Delta PE = mg\Delta h$ $\Delta PE = (2.5~kg)(9.80~m/s^2)(0.75~m)$ $\Delta PE = 18.4~J$ $18.4~J$ of work must be done on the carton. (b) We can find the change in gravitational potential energy as the litter falls: $\Delta PE = mg\Delta h$ $\Delta PE = (1.2~kg)(9.80~m/s^2)(-0.75~m)$ $\Delta PE = -8.82~J$ As the cat litter falls, the change in gravitational potential energy is $-8.82~J$. Therefore, the work done by gravity on the cat litter is $8.82~J$.