Two blocks are connected by a massless string that runs across a
frictionless pulley with a mass of 5.00 kg and a radius of 10.0 cm.
The first block with an unknown mass of m1 sits on a horizontal
surface and is also connected to a spring with a spring constant of
k = 250 N/m. The coefficient of kinetic friction between the first
block and the surface is 0.400. The second block with a mass of m2
= 6.00 kg hangs off the edge of the surface. Initially both blocks
are at rest and the spring is at its equilibrium position. After
you let the blocks go, both blocks are moving with a speed of 0.200
m/s after block 2 has fallen 10.0 cm. What is the mass of the first
block?