Answer
$K = 14.13$ $J$
Work Step by Step
The cookie transfers its spring energy to thermal and kinetic energy as it slides back
$E_s = K + E_{th}$
$-K = E_{th} - E_s $
$K = E_s - E_{th}$
$K = \frac{1}{2}kx^2 - fx$
$K = (\frac{1}{2}\times 400(0.292)^2) -( 10\times 0.292)$
$K = 17.05 - 2.92$
$K = 14.13$ $J$
