JEE Advanced 2020 Full Test 7 Paper 1

A block of mass m(=1kg) is placed on a smooth horizontal surface as shown. Its centre is tied to a string of length ℓ(=10m) and other end of the string is connected to ball of same mass. Ball is released from the position shown. It falls under gravity and then string becomes taut. The kinetic energy of block and ball just after string is taut are KEb and KEp respectively, then