# Solve the following :

Question:

A bullet travelling with a velocity of $16 \mathrm{~m} / \mathrm{s}$ penetrates a tree trunk and comes to rest in $0.4 \mathrm{~m}$. Find the time taken during the retardation.

Solution:

$\mathrm{u}=16 \mathrm{~m} / \mathrm{s} ; \mathrm{v}=0 \mathrm{~m} / 2 ; \mathrm{s}=0.4 \mathrm{~m}$

$v^{2}=u^{2}+2 a s$

$0^{2}=(1)^{2}+2(a)(0.4)$

$a=-320 m / s^{2}$

$\mathrm{v}=\mathrm{u}+$ at

$0=16+(-320) t$

$t=0.05 \mathrm{sec}$