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: Centripetal Force of a tied ball

  1. Nov 1, 2006 #1
    A 0.50 kg ball that is tied to the end of a 1.0 m light cord is revolved in a horizontal plane with the cord making a 30° angle, with the vertical (See Fig. P7.52.)

    I managed to get my answer down to solving for theta however I dont know how to do the math:

    I solved for T = mg / cos(x)
    The Fc is = Tsin(x) = (mg)[tan(x)]
    (mg)[tan(x)] = (mv^2) / r
    R (radius) = 1sin(x)

    The following equation is where I am stumped...
    sin^2(x) / cos(x) = 8 / 4.9

    Attached Files:

  2. jcsd
  3. Nov 1, 2006 #2


    User Avatar

    Are you trying to find the speed?

    Calculate Fc from Tsin(x) = (mg)[tan(x)]

    Then calculate r, and you can find v.

    I don't understand why you're stumped at that point, since you know what x is.
  4. Nov 1, 2006 #3
    sorry for not clarifying my question. I am trying to solve for x. The question is: If, instead, the ball is revolved so that its speed is 4.0 m/s, what angle does the cord make with the vertical?
  5. Nov 1, 2006 #4


    User Avatar

    OK - sorry for delay - site wouldn't let me post

    sin^2(x) / cos(x) = 8 / 4.9

    Gives you 4.9 sin^2 x = 8 cos^2 x

    Remember sin^2 x = (1 - cos^2 x) - substitute this and you should be able to solve for cos x (might be a quadratic you have to solve)
  6. Nov 1, 2006 #5
    thank you so much.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook