Exploring Circular Motion: 3.60 kg Object in P6.11

[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.

 

[Moetasim]

Circular motion is a complex concept that involves both rotational motion and centripetal force. In order to accurately solve this problem, you will need to use the correct equations and understand the physical principles at play. It is important to note that the tension in the strings will vary at different points in the motion, as the object is constantly changing direction and velocity.

To solve for the tension in the upper string, you will need to use the equation T=mg/cosθ, where θ is the angle between the string and the vertical axis. This angle can be found by using the relationship between the velocity, radius, and angle in a circular motion, as shown in the equation m(v^2/r)=Tsinθ. By solving for θ, you can then plug in the value in the equation for tension to find the correct answer.

Similarly, to solve for the tension in the lower string, you will need to use the same equations and principles. However, in this case, the angle θ will be different from the upper string, as the lower string is attached at a different position on the object.

It is important to carefully consider the variables and equations involved in circular motion problems, as well as the physical principles at play. I recommend reviewing your calculations and equations to ensure accuracy in your solution.