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
$0=16+(-320) t$
$t=0.05 \mathrm{sec}$
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