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: Uniform Circular Motion of an object

  1. Nov 19, 2007 #1
    1. The problem statement, all variables and given/known data
    A horizontal force of 210N is exerted on a 2.0kg object as it rotates uniformly on a horizontal plane with a radius of 0.9m. Calculate the speed of the object.

    2. Relevant equations
    I THINK the relevant equations for this problem are v=2[tex]\Pi[/tex]r/T and ar=v^2/r.

    3. The attempt at a solution

    My biggest problem is that for the life of me, I can't figure out how to find either the T or the v. If I knew how to do that, I could figure out the problem. I've also drawn a diagram of the problem.
  2. jcsd
  3. Nov 19, 2007 #2
    You won't need to find T. Use your equation for "ar" as you suggest, but remember Newton's Second Law... F = ma. Since you know the Force, v can be calculated. No T needed, but if you are curious, T can be calculated now that you know v!!!
  4. Nov 19, 2007 #3


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    All you need to know is that the radial acceleration (or centripetal acceleration ) is v^2/r, as you have noted. Then use newton's 2nd law in the radial (centripetal) direction to calculate v, the tangential speed .
  5. Nov 19, 2007 #4
    In this case, would my F=m(a) be 2.0(210)?

    I'm thinking I need to find "a" first... perhaps a=Fnet/m?
    Last edited: Nov 19, 2007
  6. Nov 19, 2007 #5
    No...F = 210, m = 2.0, a is given by the equation you have stated...v^2/r
  7. Nov 20, 2007 #6

    F=ma and a=v^2/r... F=m(v^2/r)




    v=sqrt 210(.9)/2.0

    v= 9.7 m/s^2
  8. Nov 20, 2007 #7
  9. Nov 20, 2007 #8
    thank you guys so much :D
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook