25.0kg would give a tension force in the string of about 250N (taking g=10, from 9.81)For a mass of 53kg rotating horizontally in a circle of radius 50.8, the string has to be able to supply a centripetal force to keep the mass moving in circular motion.Centripetal force F = m v^2/r. If the string breaks at about 250N, then it will break if250=53 v^2/50.8 m/ssqrt(250x50.8/53) = vSince there don't seem to be any "easy numbers" in the q, I guess it wants the 9.81 version of g.
