# Frictional coin sliding on turntable

1. Oct 20, 2007

### Umphreak89

A 5.0 g coin is placed 22 cm from the center of a turntable. The coin has static and kinetic coefficients of friction with the turntable surface of µs = 0.80 and µk = 0.50. What is the maximum rpm that the turntable could speed up to without the coin sliding off?

m = .005 kg
r = .22 m
µs = 0.8

Equations found..
v = angular velocity * r
Force(net) = m(v)^2 / r

Inertia > µs N when coin slips (?)

I believe this gets set equal to mg (Normal Force) but I haven't been able to generate the correct answer multiplying µs as a coefficient of either side.

I'm not sure what isn't being accounted for, what do I do?

Last edited: Oct 20, 2007
2. Oct 20, 2007

### Staff: Mentor

You're heading in the right direction. Answer these questions:
(1) What force provides the centripetal force on the coin?
(2) What's the maximum value of that force?

Use that maximum value of force in your centripetal force equation to calculate the maximum speed. Then express that answer in rpm.

Do Not Double Post!

Last edited: Oct 20, 2007