Question

Determine the average force necessary to stop a bullet of mass $20g$ and a speed of $250{ms}^{-1}$ as it penetrates wood to a distance of $12.5cm.$

Answer 1

$a=\frac{v^2-u^2}{2s}=\frac{{\left(250\right)}^2-{\left(0\right)}^2}{2\times \left(12.5\right)\times {10}^{-2}}=\frac{62500\times {10}^2}{25}=250000m/s^2$

force required $=ma$

$=20\times {10}^{-3}\times 25\times {10}^4=5000N=5KN$.