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September 18, 2019

Solution to problems – class 9 – Set 1 Q 57

Problem Statement

57) A ball X of mass 1 kg travelling at 2 m/s has a head-on collision with an identical ball Y at rest.

X stops and Y moves off.

Calculate the velocity of Y after the collision.


Initial momentum of X = 1×2 kg m/s = 2 kg m/s …………….(i)

After collision X stops and Y moves off, with say V m/s

Y is identical to X. So its mass is also 1 kg

So final momentum = 1 x V =V……………….(ii)

As per law of conservation of momentum,
V = 2

Here we get the value of velocity of Y as 2 m/s

Question Set – Physics Problems for grade 9

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