# Centrifugal force coins

Two coins are on a turntable that steadily speeds up, starting from rest, with a ccw rotation. Which coin flies off the turntable first?

Coin 2 is further away than coin 1.

MY ATTEMPT:

I believe centrifugal acceleration is done by friction. So fs=us*m*g. Fc=mv^2/r.
Then, v=sqroot(us*g*r).
Suppose coin 2 is at radius 2(r1), (r1) being the distance from center of coin 1.
angular velocity 1= r1(sqroot(us*g))
angular velocity 2=2r1(sqroot(us*g))

So, I conclude that coin 1 must be thrown off first. HOWEVER, the answer manual says it is coin 2, which is an obvious answer for me too. But, I can't seem to be able to prove it.

## Answers and Replies

nasu
Gold Member
Your expressions for angular velocity are not right.
Check again.
The velocity (v) is OK.

Ok, I rearranged it. I now understand! v=wr indeed!
Is there any easier way to think about this problem?