Verified Solution • 2025–26 Session moderate

QJEEM19Phd3f5: JEE Main 2019 Physics - Class 11 JEEM19Phd3f5 Solution: A body of mass 2 kg makes an eleastic collision with a second…

A body of mass 2 kg makes an eleastic collision with a second body at rest and continues to move in the original direction but with one fourth of its original speed. What is the mass of the second body ?

Multiple Choice Options

  • A 1.2 kg
  • B 1.0 kg
  • C 1.8 kg
  • D 1.5 kg

Step-by-Step Verified Solution

By conservation of linear momentum:

2v0=2(v04)+mv⇒2v0=v02+mv2{v_0} = 2\left( {{{{v_0}} \over 4}} \right) + mv \Rightarrow 2{v_0} = {{{v_0}} \over 2} + mv

⇒3v02=mv  ...(1)\Rightarrow {{3{v_0}} \over 2} = mv\,\,...(1)

Since collision is elastic

Vseparation=Vapproch{V_{separation}} = {V_{approch}}

⇒v−v04=v0⇒m=65=1.2 kg\Rightarrow v - {{{v_0}} \over 4} = {v_0} \Rightarrow m = {6 \over 5} = 1.2\,kg

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