Question

A ball of mass $100\text{g}$ and another ball of mass $120\text{g}$ moves towards each other with speeds $6\text{m/s}$ and $5\text{m/s}$ respectively. If they stick to each other after colliding, what would be the velocity of the combined mass after the collision?

• A. $0\text{m/s}$
• B. $2\text{m/s}$
• C. $4\text{m/s}$
• D. $6\text{m/s}$

Answer 1

The correct option is A $0\text{m/s}$

Before collision,
Initial linear momentum, $p_i=0.1\times 6+0.12\times (-5)=0$


After collision, suppose speed of combined mass is $v$, then,
Final linear momentum, $p_f=(0.1+0.12)v=0.22v$

From Law of Conservation of Linear Momentum,
$p_i=p_f$

$\Rightarrow 0=0.22v$

$\Rightarrow v=0\text{m/s}$