Center of Mass Momentum a question bank (Physics)

A block of mass ‘m’ moving on a frictionless surface at speed ‘v’ collides elastically with a block of same mass, initially at rest. Now the first block moves at an angle ‘θ’ with its initial direction and has speed ‘$v_1$’ . The speed of the second block after collision is

If the radius of the circular path and frequency of revolution of a particle of mass m are doubled, then the change in its kinetic energy will be ( $E_i$ and $E_f$ are the initial and final kinetic energies of the particle respectively,)