A particle of mass m with an initial velocity ûi collides perfectly elastically with a mass 3m at rest. It moves with a velocity v̂j after collision, then, v is given by

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(3) v=u/(√2). Momentum: 3m⃗V=mûi-mv̂j⇒⃗V=(ûi-v̂j)/3. Energy: u²=v²+3((u²+v²)/9)⇒3u²=3v²+u²+v²⇒2u²=4v². v=u/(√2).

A particle of mass m with an initial velocity ûi collides perfectly elastically with a mass 3m at rest. It moves with a velocity v̂j after collision, then, v is given by

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