Question

When the bob of a simple pendulum of length ‘l’ is released from its horizontal position, it strikes a block of equal mass (m) lying on a frictionless table as shown in the figure. The bob transfers all its momentum to the block. The kinetic energy of the block will be (g = acceleration due to gravity at the place)(A) mgl (B) 2mgl (C) mg 2 l (D) 0 ​

Answer 1

Explanation:

Correct option is C)

When the bob reaches its lowest point it has kinetic energy which is equal to the work done by gravity while coming down.

K.E=m×g×l

When it strikes the block of same mass elastically the law of conservation of momentum gives that the velocity will be exchanged

Now, as their masses are same and also velocity is exchanged , the kinetic energy of the block will be:

KE=m×g×l