Question

A 1 kg ball moving at $12m{s}^{-1}$ collides head-on with a $2kg$, ball moving in the opposite direction at $24m{s}^{-1}$. If $e=2/3$ the velocities after impact are respectively.

• A. $-28m{s}^{-1}$,$-4m{s}^{-1}$
• B. $28m{s}^{-1}$,$-4m{s}^{-1}$
• C. $-28m{s}^{-1}$,$4m{s}^{-1}$
• D. $28m{s}^{-1}$,$4m{s}^{-1}$

Answer 1

The correct option is A $-28m{s}^{-1}$,$-4m{s}^{-1}$

Using momentum conservation,
$-36=v_1+2v_2$

$e=\frac{v_1-v_2}{36}=\frac{2}{3}$

$v_1-v_2=-24$
$\Rightarrow v_1=-28$ m/s
$v_2=-4$ m/s