Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Circular motion of a coin

  1. Mar 6, 2010 #1
    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. jcsd
  3. Mar 6, 2010 #2


    User Avatar
    Homework Helper

    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)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook