centripetal acceleration= friction
m*w^2 r = mu*mg
changing 50 rpm to rad/sec
mu=w^2 r/g=(50*2PI/60)^2 * .12
which is not your answer.
Check my thinking.
ok I thought centripetal force was equal to
m ac
were ac is the centripetal acceleration
which is equal to v^2 divided by r I don\'t recall it being equal to times r