question_answer

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/s

B) 1.5 m/s

C) - 0.15 m/s

D) None of the above

Correct Answer: C

Solution :

[c]

MI of figure (ii) is smaller hence acceleration is greater.

Initial linear momentum of system

\[={{m}_{A}}{{\vec{v}}_{A}}+{{m}_{B}}{{\vec{v}}_{B}}=0.2\times 0.3+0.4\times {{v}_{B}}\]

Finally both balls come to rest

\[\therefore \]  final linear momentum = 0

By the law of conservation of linear momentum

\[0.2\times 0.3+0.4\times {{v}_{B}}=0\]

\[\therefore \]      \[{{v}_{B}}=-\frac{0.2\times 0.3}{0.4}=-0.15\,\,m/s.\]