Answer
(a) $18.4~J$ of work must be done on the carton.
(b) The work done by gravity on the cat litter is $8.82~J$
Work Step by Step
(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 $8.82~J$.
