# Homework Help: Centripetal force problem

1. Oct 22, 2005

### smileyjen523

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. Oct 22, 2005

### daniel_i_l

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:)

3. Oct 22, 2005

### daniel_i_l

sorry, I wanted to say that you dont need the SPEED to find the centripetal force.

4. Oct 22, 2005

### Fermat

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.