The bob of a simple pendulum (mass m and length l) dropped from a horizontal position strikes a block of the same mass elastically placed on a horizontal frictionless table. The K.E. of the block will be : 

\(mgl\)

P.E. of bob at point A = mgl

This amount of energy will be converted into kinetic energy

$\therefore$ K.E. of bob at point B = mgl

Since Collision is elastic hence bob will come to rest and block will start moving with speed same as that of bob.

$\Rightarrow \text{K.E of Block will be } mgl$