1. The problem statement, all variables and given/known data A mass m1 on a horizontal shelf is attached by a thin string that passes over a frictionless pulley to a 2.8 kg mass (m2) that hangs over the side of the shelf 1.6 m above the ground. The system is released from rest at t = 0 and the 2.8 kg mass strikes the ground at t = 0.81 s. The system is now placed in its initial position and a 1.2 kg mass is placed on top of the block of mass m1. Released from rest, the 2.8 kg mass now strikes the ground 1.3 seconds later. (a) Determine the mass m1. kg (b) Determine the coefficient of kinetic friction between m1 and the shelf. 2. Relevant equations v^2=v(initial)^2-2ad Sum F=ma F(kinetic)=u(kinetic)mg 3. The attempt at a solution I applied F=ma to m1 and m2 for x and y m1: x: T-f(kinetic)=0; T=f(kinetic); T=u(kinetic)m1*g y: F(normal)-m1*g=0; F(normal)=m1*g; f(kinetic)=u(kinetic)m1*g m2: x: T=m2g; m2g=u(kinetic)m1*g The next step would be to solve m2g=u(kinetic)m1*g for u(kinetic) or m1 but without one of these I can't find either so I am stuck here.