A massless string is wrapped around a solid cylinder as shown in the diagram. A block of mass 2kg hangs from a string. When released, the block falls a distance of 82 cm in 2.0 seconds. Calculate the mass using the conservation of mechanical energy.
d=speed(i) + 1/2at^2
V(f)=v(i) + at
PE=KE(block) + KE(cylinder)
mgy=1/2mv^2 + 1/2(1/2MR^2)(v/r)^2
The problem is that I do not know how to find R? Please help!