# Homework Help: Circular motion!

1. Feb 20, 2008

### zcabral

***circular motion!***

1. The problem statement, all variables and given/known data
http://www.webassign.net/pse/p6-11.gif
A 3.60 kg object is attached to a vertical rod by two strings as in Figure P6.11. The object rotates in a horizontal circle at constant speed 7.20 m/s.

(a) Find the tension in the upper string.

(b) Find the tension in the lower string.

2. Relevant equations

T=mg/costheta
m(v^2/r)=Tsintheta

3. The attempt at a solution

I tried to solve for r and i got 1.32 but when i plugged it into the equation for tension it said it was wrong. i tried to solve for theta and got 41.3 in order to plug into the equation and it was wrong as well. what am i doing wrong??

2. Feb 20, 2008

### hage567

I think you are forgetting there are two strings. You can't use your equation and do each string separately. You need two different tension forces in your equations. Draw a free body diagram of the ball and sum up the forces in each direction like you would do for any other force problem.