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Question: Two solid rubber balls A and B having masses 200 and 400 gm respectively are moving in opposite dire...

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

– 0.15 m/sec

Explanation

Solution

Initial linear momentum of system

= mAv⃗A+mBv⃗Bm _ { A } \vec { v } _ { A } + m _ { B } \vec { v } _ { B }

= 0.2 × 0.3 + 0.4 × vB

Finally both balls come to rest

∴ final linear momentum = 0

By the law of conservation of linear momenum

0.2 × 0.3 + 0.4 × vB = 0

∴ vB=−0.2×0.30.4=−0.15 m/sv _ { B } = - \frac { 0.2 \times 0.3 } { 0.4 } = - 0.15 \mathrm {~m} / \mathrm { s }