Question

Two solid rubber balls A and B having masses 200 and 400 gm respectively are moving in opposite directions with velocity of A equal to 0.3 m/s. After collision the two balls come to rest, then the velocity of B is

• A. 0.15 m/sec
• B. 1.5 m/sec
• C. - 0.15 m/sec
• D. None of the above

Answer 1

The correct option is C. - 0.15 m/sec

Initial linear momentum of system = $m_A{\overrightarrow{v}}_A+m_B{\overrightarrow{v}}_B$

= $(0.2\times 0.3)+(0.4\times v_B)$

Finally both balls come to rest

$\therefore$ final linear momentum = 0

By the law of conservation of linear momenum

$(0.2\times 0.3)+(0.4\times v_B)=0$

$\therefore$ $v_B=-\frac{0.2\times 0.3}{0.4}=-0.15m/s$.