# Circular motion

1. Mar 6, 2010

### Cfem

1. The problem statement, all variables and given/known data
A 4.80 g coin is placed 11.0 cm from the center of a turntable. The coin has static and kinetic coefficients of friction with the turntable surface of us = 0.770 and uk = 0.400.

What is the maximum angular velocity with which the turntable can spin without the coin sliding? (In rad/s)

2. Relevant equations

Ff = FN(u)
Fa = (mv^2)/r

3. The attempt at a solution

I've always been a little foggy on rotational motion, but for this I converted the grams to kilograms and the centimeters to meters, then set the friction equal to the acceleration:

(.0048)(9.8)(.77) = [(.0048)(v^2)]/.11

Which gave me a v of .911 rad/s. I'm not sure what I did wrong/what I'm missing.

2. Mar 6, 2010

### rock.freak667

the 'v' you get is the linear velocity, you need to use ω=v/r to get the angular velocity.

(Note: I did not check your answer to see if that is what you did, but your response implied that you put 'v' as the angular velocity)