A mass m1 on a horizontal shelf is attached by a thin string that passes over a frictionless pulley to a 2.5 kilogram mass (m2) that hangs over the side of the shelf 1.5 meter above the ground. The system is released from rest at t = 0 and the 2.5 kilogram mass strikes the ground at t = 0.71 second. The system is now located in its initial position and a 1.2 kilogram mass is located on top of the block of mass m1. Released from rest, the 2.5 kilogram mass now strikes the ground 1.3 seconds later.
(a) Compute the mass m1.
(b) Find the coefficient of kinetic friction between m1 and the shelf.