Question

A bullet of mass $50g$ moving with an initial velocity $100m{s}^{-1}$, strikes a wooden block and comes to rest after penetrating a distance 2 cm in it. Calculate :

1. initial momentum of the bullet
2. final momentum of the bullet,
3. retardation caused by the wooden block, and
4. resistive force exerted by the wooden block

Answer 1

Given,

$Mass,m=0.05kg$ Initial ve locity, v=100m/s,s=0.2m$

i) Initial momentum $=mu=0.05\times 100=5Ns$

ii) Let $a$ be the acceleration, then

$v^2=u^2+2as\Rightarrow 0={100}^2+2a\times 0.02\Rightarrow a=-2.5\times {10}^{5}m/s^2$

So retardation acceleration is $2.5\times {10}^{5}m/s^2$

iv) $F=ma=0.05\times -2.5\times {10}^5=12500N$