Question

A $10g$ bullet is fired at a plank of wood with a speed of $200m{s}^{-1}$. After passing through the plank, which is $1m$ thick, the speed of the bullet reduces to $100m{s}^{-1}$. Find the average resistance offered by the plank.

Answer 1

Using $v^2=u^2-2as$ and putting $v=100m/s$, $u=200m/s$ and $s=1m$

we get retardation $a=1.5\times {10}^{4}m/s^2$

so average resitance offered $F=ma=\left(10/1000\right)1.5\times {10}^4=150Kg$ $m/s^2=150Newton$