1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
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: Torque in circular motion

  1. Nov 8, 2009 #1
    1. The problem statement, all variables and given/known data
    When play is pressed, a cd accelerates uniformly from rest to 500 rev/min in 3.0 revolutions. If the Cd has a radius of 5.5 cm, and a mass of 20 g, what is the torque?

    2. Relevant equations
    not sure, this is my problem. i think its torque=angular acceleration*inertia. but i dont know how to turn "500 rpm in 3.0 revolutions" into angular acceleeration

    3. The attempt at a solution
    nothing, i dont how to make the equations work
  2. jcsd
  3. Nov 8, 2009 #2
    You have your analogy from linear kinematics equations to rotational motion equations.

    a = delta v / delta t

    So the same is true for rotational acceleration, and change in rotational velocity
  4. Nov 8, 2009 #3
    but how does torque fit into this equation?
  5. Nov 9, 2009 #4
    You can use: [tex]\omega^{2}=2\alpha s[/tex] , where [tex]s=2\pi r * 3[/tex] (3 times the circumference)

    and 500 [tex]rev/min=4770 rad/sec[/tex]
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook