Question

Ball A of mass $5kg$ travelling at $6m{s}^{-1}$collides with another ball B of mass $2kg$ travelling at $2m{s}^{-1}$ in the same direction. After collision, the velocity of ball A reduces to $2m{s}^{-1}$. Calculate the velocity of ball B after the collision.

• A. $10m{s}^{-1}$
• B. $12m{s}^{-1}$
• C. $6m{s}^{-1}$
• D. $8m{s}^{-1}$

Answer 1

The correct option is B

$12m{s}^{-1}$

Given:
Mass of ball A $\left(m_1\right)$ = $5kg$
Mass of ball B $\left(m_2\right)$ = $2kg$
Initial velocity of ball A $\left(u_1\right)$ = $6m{s}^{-1}$
Initial velocity of ball B $\left(u_2\right)$ = $2m{s}^{-1}$
Final velocity of ball A $\left(v_1\right)$ = $2m{s}^{-1}$
According to the law of conservation of momentum,
Initial momentum of the system = Final momentum of the system
$\Rightarrow$$m_1{u}_1+m_2{u}_2=m_1{v}_1+m_2{v}_2$
$\Rightarrow$$5\times 6+2\times 2=5\times 2+2\times v_2$
$\Rightarrow$ $v_2=12m{s}^{-1}$