# Centripetal Force with angle problem

1. Oct 26, 2011

### taxidriverhk

1. The problem statement, all variables and given/known data
Consider the figure below, a ball of mass m=0.100 kg tied by a string of 0.100 m travels in a circular motion with 2 revolutions per second. Find the angle θ that keeps the ball stationary.
Given: m = 0.100 kg, v = 2 rev/sec L = 0.100 m (radius?)
[PLAIN]http://img192.imageshack.us/img192/9518/unledrht.jpg [Broken]

2. Relevant equations
FC = $\frac{mv^{2}}{r}$

3. The attempt at a solution
Let T be the tension force.
y: Tcosθ - mg = 0
x: Tsinθ = mv2/r

The problem is I am not sure if the setup above is right, and should I take the length of the string as the radius? or rsinθ?
Hope you guys can help me, thank you very much, I will be extremely appreciated!!

Last edited by a moderator: May 5, 2017
2. Oct 27, 2011

### Andrew Mason

I don't understand the question. If the ball is moving it is not stationary. Is this a pendulum? Is it horizontal or vertical? Please give us the exact wording of the question.

AM