Ball A of mass 6 kg moving with a velocity of 20 ms−1 collides with another ball B of mass 2 kg moving in the opposite direction with a velocity of 10 ms−1. After the collision, ball A comes to rest. Find the speed of ball B after collision.
A
10 ms−1
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B
20 ms−1
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C
30 ms−1
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D
50 ms−1
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Solution
The correct option is D 50 ms−1 By the law conservation of momentum: mAuA + mBuB = mAvA + mBvB
6 × 20 + 2 × (-10) = 6 × 0 + 2 × vB
(Velocity is a vector quantity. Since the balls are approaching from opposite directions, uB is negative.) vB = 6×20−202 vB = 50 ms−1