Question

A bullet moving with a velocity of $200cm/s$ 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. $100cm/s$
• B. $136.2cm/s$
• C. $300cm/s$
• D. $250cm/s$

Answer 1

The correct option is C $300cm/s$

$u=2m/s$ and $v=0$ $s=.04m$ so retardation $a=\frac{u^2-v^2}{2s}=50m/s^2$

to travel a distance $s=0.09m$ in the same block the velocity needed $u$ will be given by $v^2=u^2-2as$

or $u=\sqrt{(2as+0)}=\sqrt{2\times 50\times .09}=3m/s=300cm/s$