Question

A bullet having a mass of 10 g and moving with a speed of 1.5 $m{s}^{-1}$, penetrates a thick wooden plank of mass 90 g. The plank was initially at rest. The bullet gets embedded in the plank and both move together. Determine their velocity.

• A. $0.10m{s}^{-1}$
• B. $0.15m{s}^{-1}$
• C. $0.15m{s}^{-2}$
• D. $0.10m{s}^{-2}$

Answer 1

Answer: (B)

. $0.15m{s}^{-1}$.

Given,

the mass of bullet $m_1=10g=0.01kg$,

initial speed of bullet $u_1=1.5m{s}^{-1}$,

mass of wooden plank $m_2=90g=0.09kg$,

final velocity of plank + bullet = $v$ and

initial speed of wooden plank $u_2=0$

Here, we apply the law of conservation of momentum, i.e., Final momentum = Initial momentum.

$m_1{u}_1+m_2{u}_2=m_{1}v+m_{2}v$

$0.01\times 1.5+0.09\times 0=0.01\times v+0.09\times v$

$0.015=0.1v$

On solving $v=0.15m{s}^{-1}$.