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 problem

  1. Oct 22, 2005 #1
    a small ball of mass 38g is suspended from a string a length 59cm, and whirled in a circle lying in the horizontal plane. The acceleration of gravity is 9.8m/s2. if the string makes an angle of 31o with the vertical, find the centripetal froce experienced by the ball.

    here's the diagram:(the best i can do) it looks like a triangle when i view it but then it goes all weird in the actual view. sorry.
    l\
    l \
    l \ 59cm
    l \
    l \
    l O=38g

    then there's the dotted lined circle drawn, but i don't know how to do that here.

    ok, so first i found the radius using trig and got it to be 30.3872m. then i was going to find velocity, but then i don't know how to do that. help would be greatly appreciated. thanks sooo much.
     
  2. jcsd
  3. Oct 22, 2005 #2

    daniel_i_l

    User Avatar
    Gold Member

    You don't need the force to fing the centripetal force. The CF is equal to the tension of the the string along the x-axis. Since you know the angle of the string, all that you need is to find the tension of the string:
    Fc = Tsin(31)
    since the ball has no acceleration along the y-axis you can write:
    Tcos(31) = 38*9.8 (mg)

    and find the tension:)
     
  4. Oct 22, 2005 #3

    daniel_i_l

    User Avatar
    Gold Member

    sorry, I wanted to say that you dont need the SPEED to find the centripetal force.
     
  5. Oct 22, 2005 #4

    Fermat

    User Avatar
    Homework Helper

    Code (Text):

    l\
    l \
    l  \  59cm
    l   \
    l    \
    l     \[SIZE="5"]O[/SIZE]=38g
    enclose your diagram in [ code ] tags. It helps formatting a bit, though you may still have to nudge it.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook