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
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Problems Set – grade 9