Calculate minimum speed of an object in circular motion

[johnarma]

Homework Statement

Picture of my object
http://img147.imageshack.us/my.php?image=circlekz1.png
How do i calculate the least amount of speed ( aka vmin) an object has at point z without breaking the string or making it go slack. I also need to show how I got it.

There should be little to no numbers used. This is mostly variables and in putting vmin on one side and showing how i got there.

Homework Equations

The Attempt at a Solution

 

[LowlyPion]

Homework Statement

Picture of my object
http://img147.imageshack.us/my.php?image=circlekz1.png
How do i calculate the least amount of speed ( aka vmin) an object has at point z without breaking the string or making it go slack. I also need to show how I got it.

There should be little to no numbers used. This is mostly variables and in putting vmin on one side and showing how i got there.

Homework Equations

The Attempt at a Solution

Welcome to PF.

Draw a force diagram and identify what forces at z need to be in balance to satisfy the minimum speed.

 

[johnarma]

the only 2 forces are t and w but those are going in the same direction, there is no force in an opposing direction!

 

[LowlyPion]

the only 2 forces are t and w but those are going in the same direction, there is no force in an opposing direction!

And what again is the "T"?

How do you calculate T if it was horizontal?