1. Not finding help here? Sign up for a free 30min 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!

Tethebal| problem, radial acceleration, angle of ball orbit

  1. Nov 24, 2007 #1
    1. The problem statement, all variables and given/known data

    This is a concept/procedure question. I am playing teth3rbalI with a 1 kilogran ball and it is tied to a meterlong string. When I hit the ball it circles the pole at 1.6 Hz. Find the anglethat the string makes with thepole.

    2. Relevant equations


    3. The attempt at a solution

    So I found the period for one cycle but that's basically it and I'm stuck without a radius or at least a velocity to go by. What am I overlooking?

    Attached Files:

  2. jcsd
  3. Nov 24, 2007 #2

    Shooting Star

    User Avatar
    Homework Helper

    The whirling string has to make an angle, say 'x', with the vertical in the downward direction. It lies on a cone, whose semi-vertical angle is 'x'. If 'T' is the tension in the string, then mg=T*cos(x). The centipetal force is T*sin(x). The mass m travels in a horizontal plane.

    Now you try for a while.
  4. Nov 24, 2007 #3

    k so wow, i' not getting very far at all on this.

    since Tcos(x) = mg then Tcos(x) = 9.8 N and since T sin(x) = centripedalforce then Tsin= 1kg((4[tex]\pi[/tex][tex]^{2}[/tex]r)/(.625[tex]^{2}[/tex]))

    I'm slightly nervous proceeding since my next move would be to do a pythagoras of 9.8[tex]^{2}[/tex] + ((4[tex]\pi[/tex][tex]^{2}[/tex]r)/TimePeriod[tex]^{2}[/tex])[tex]^{2}[/tex] = T[tex]^{2}[/tex] which doesn't seem right nor does it make me any more confident.
    Last edited: Nov 24, 2007
  5. Nov 24, 2007 #4
    kk think i got it but does the mass cancel out?
  6. Nov 25, 2007 #5

    Shooting Star

    User Avatar
    Homework Helper

    It'd be neater if you didn't write the values of g etc in every step. Use symbols and plug in the values later.

    Yes, the mass cancels out.

    The centripetal force is m*w^2*r= T*sin x.

    tan x = Tsin x/Tcos x = mw^2*r/mg =rw^2/g.

    You know the value of r, and w is given.
  7. Nov 25, 2007 #6


    User Avatar
    Staff Emeritus
    Science Advisor

    If you look at Shooting Star's post this should become apparent.

    It would also help if you formatted your posts in a more readable way. For example [ tex] [ /tex] tags should be used for LaTeX set on its own, whereas you should use [ itex] [ /itex] tags for inline maths. Furthermore, it would help if you either did all your equations in tex, or none of them, since that would prevent strange mixed formatting.

    Just a few thoughts, anyway.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Tethebal| problem, radial acceleration, angle of ball orbit