Circular motion and tension of a stone problem

[Coco12]

1. Homework Statement [/b]


A stone mass 284g is twirled at a constant speed 12.4m/s in a vertical circle of radius 0.850m. Find the tension in the string at the top and at the bottom of the revolution. What is the maximum speed the stone can have if the string will break when the tension reaches 33.7N

Homework Equations

FC=mv^2/r

The Attempt at a Solution

I know how to solve for tension in the bottom: ft=FC+fg

I thought for the tension at the top: ft=fg


However when I plugged in the info, did not get the ans: 48.6N

Also for the maximum speed, I use the centripetal force formula- and manipulated it to get v=sqrt 33.7N*.850m/.284kg to get 10.04m/s
However the ans is 9.62??

 

[tiny-tim]

Hi Coco12!

(try using the X² and X₂ buttons just above the Reply box )

I know how to solve for tension in the bottom: ft=FC+fg

Yes, but why?

(apply the same reasoning to the top)