Hockey puck?

Question

A hockey puck of mass m is attached to a string that passes through a hole in the center of a table. The hockey puck moves in a circle of radius r. Tied to the other end of the string, and hanging vertically beneath the table, is a mass M. Assuming the tabletop is perfectly smooth, what speed must the hockey puck have if the mass M is to remain at rest? (Use g for acceleration due to gravity, and m, r, and M as necessary.)

Answer 1

The weight of mass M acts on mass m as centripetal, so:

Fc=W

m*v^2/r=M*g

v^2=(M*g)/m

v=sqr(M*g/r)

Hope it helps