On a frictionless surfaces, a block of mass M moving at speed v collides elastically with another block of…

On a frictionless surfaces, a block of mass M moving at speed v collides elastically with another block of same mass M which is initially at rest. After collision the first block moves at an angle θ to its initial direction and has a speed v3 . The second block's speed after the collision is:
  1. 34v
  2. 32v
  3. 32v
  4. 223v

Solution


In elastic collision energy of system remains same. so, \((\mathrm{KE})_{\text {before collision }}=(\mathrm{KE})_{\text {after collision }}\)
Let speed of second body after collision is \(\mathrm{v}^{\prime}\).
$\begin{aligned} & \frac{1}{2} Mv^2+0=\frac{1}{2} M\left(\frac{v}{3}\right)^2+\frac{1}{2} M\left(v^{\prime}\right)^2 \\ & \Rightarrow v^{\prime}=\frac{2 \sqrt{2}}{3} v \end{aligned}$

Asked in: NEET 2015 (Phase 2)

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