A particle of mass m with an initial velocity u i ^ collides perfectly elastically with a mass 3   m at…

A particle of mass m with an initial velocity ui^ collides perfectly elastically with a mass 3 m at rest. It moves with a velocity vj^ after collision, then, v is given by 
  1. v=23u
  2. v=u3
  3. v=u2 
  4. v=16u

Solution

From momentum conservation

mui^+0=mvj^+3mv'

v'=u3i^-v3j^

From kinetic energy conservation 12mu2=12mv2+12(3m)u32+v32

solving v=u2

Asked in: JEE Main 2020 (02 Sep Shift 1)

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