Q. A bullet moving with a velocity of 200 $cm/s$ penetrates a wooden block and comes to rest after traversing $4cm\ $inside it. What velocity is needed for travelling distance of $9cm$ in same block
A) $100\ cm/s$
B) $136.2cm/s$
C) $300cm/s$
D) $250\ cm/s$
Explanation
(c) As $v^{2}$=$v^{2} - 2as \Rightarrow u^{2} = 2as$ ($\therefore v = 0$)
$\Rightarrow u^{2} \propto s \Rightarrow \frac{u_{2}}{u_{1}} = \left( \begin{array}{r}
\frac{s_{2}}{s_{1}} \\
\
\end{array} \right)^{1/2}$
$\Rightarrow u_{2} = \left( \begin{array}{r}
\frac{9}{4} \\
\
\end{array} \right)^{\frac{1}{2}}u_{1} = \frac{3}{2}u_{1} = 300m/s$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.