Question

The mass of the bullet is $2kg$ and velocity of bullet after firing is $25m{s}^{-1}$. If initial velocity of gun and bullet is zero, what is the final momentum of gun after firing?

• A. $-25kgm{s}^{-1}$
• B. $-25kgm{s}^{-1}$
• C. $50kgm{s}^{-1}$
• D. $-50kgm{s}^{-1}$

Answer 1

The correct option is D

$-50kgm{s}^{-1}$

Here, mass of the bullet, $m_1=2kg$, velocity of bullet $v_1=25m{s}^{-1}$
Let mass of the gun be $m_2$ and velocity of the gun be $v_2$
Given total initial momentum is zero because initial velocity of the gun and the bullet is zero.
According to law of conservation of momentum,
$\left(m_1{u}_1\right)+\left(m_2{u}_2\right)=\left(m_1{v}_1\right)+\left(m_2{v}_2\right)$
$\Rightarrow 0=(2\times 25)+\left(m_2{v}_2\right)$
$\Rightarrow \left(m_2{v}_2\right)=-50kgm{s}^{-1}$
$\therefore$Final momentum of the gun after firing is $-50kgm{s}^{-1}$