Question

A bullet of mass 20 g is fired from a rifle with a velocity of 800 $m{s}^{-1}$. After passing through a mud wall 100 cm thick, velocity drops to 100 $m{s}^{-1}$. What is the average resistance of the wall? (Neglect friction due to air and work of gravity)

Answer 1

Initial velocity $u=800m/s$ and velocity after travelling a distance $s=100cm=1m$ is $v=100m/s$

so the acceleration, $a$ from the equation, $v^2=u^2-2as$

will be $a=\frac{640000-10000}{2}=270000m/s^2$

so the average(because the resistance will not be uniform ) resistive force will be $F=ma=0.02Kg\times 270000m/s^2$

or $F=5400Newton$