A bullet of mass $50\ g$ travelling at $500\ m/s$ penetrates $100\ cm$ into a wooden block. Find the average force exerted on the block.

Mass, $m = 0.05\ kg$

Initial velocity, $u = 500\ m/s$

Distance covered, $S = 100 cm = 1\ m$

Final velocity $v=0$

Now, from the equation of motion

${{v}^{2}}-{{u}^{2}}=2as$

$0-{{\left( 500 \right)}^{2}}=2\times a\times 1$

$a=-125000\,m/{{s}^{2}}$

Now, the average force exerted on the block

$F=ma$

$F=0.05\times 125000$

$F=6.25\times {{10}^{3}}$

$F=0.625\times {{10}^{4}}\,N$

Hence, the average force is $0.625\times {{10}^{4}}\,N$