Answer
$4000~joules $
Work Step by Step
$ K=cv^{2}$ and $ c=\frac{1}{2}m $ (where m is the mass and c is a constant in this problem).
When $ v=18m/sec $, $ K=12960joules $, we have $ c=\frac{12960}{18^{2}}=40joules\cdot sec^{2}/m^{2}$
Therefore, when $ v=10m/sec, K=40\times 10^{2}=4000joules $
