A bullet of mass m and velocity v passes through a pendulum bob of mass M and emerges with velocity v/2 (figure). The pendulum bob is at the end of a string of length ℓ. What is the minimum value of v (in m/s) such that the pendulum bob will swing through a complete circle ? (Take : ℓ = 2m, M = 1kg, m = 10 gm.)