A metallic bob X of mass m is released from position A. It collides elastically with another identical bob Y placed at rest at position B on a horizontal frictionless table. The angle AOB is 30^{\circ}.<br>How high does the bob X rise immediately after the collision ?

  1. A. To the same height as that of position A on the other side in the same trajectory
  2. B. To half the height as that of position A on the other side along the same trajectory
  3. C. The same height at position A
  4. D. It stops at position B ✓

Correct Answer: D. It stops at position B

Explanation

In an elastic, head-on collision between two identical bodies where one is at rest, they exchange their velocities. Thus, bob X transfers its kinetic energy to bob Y and completely stops at position B.

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