What are the tensions in the strings of a 3.60 kg object in circular motion?

[zcabral]

***circular motion!***

Homework Statement

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.

Homework Equations

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

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??

 

[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.