Answer
$f = 212.3$N
Work Step by Step
$\Delta E = fh$
$f = \frac{\Delta E}{h}$
$f = \frac{ -1(\Delta K + \Delta U)}{h}$
$\Delta K$ and $ \Delta U$ were solved in part (a) and part (b)
$f = \frac{ -(392 -2940)}{h}$
$f = \frac{ -392 + 2940}{h}$
$f = \frac{ -392 + 2940}{12}$
$f = \frac{ 2548}{12}$
$f = 212.3$N
