A pendulum consists of a compact .40 kilogram bob attached to a string of length 1.6 m. A block with mass m1 rests on a horizontal frictionless surface. The pendulum is released from rest at an angle of 53o with the vertical. The bob collides elastically with the block at the lowest point in its arc. Following the collision, the maximum angle of the pendulum with the vertical is 5.73o. Find what the mass m.