# Centripetal Force Minimum Period Question

1. Nov 14, 2012

### Lax0

1. The problem statement, all variables and given/known data
A boy ties a 3.00kg rock to a 0.70 m string and begins spinning it around in a horizontal circle at a constant speed. If the string will break if the tension is greater than 80.0 N, what is the minimum period for the rock to spinning in a circle. How do i solve this?

2. Relevant equations

m4∏^(2 ) r/T^2

3. The attempt at a solution
80.0= (3.00)4∏^(2)(0.70)/T^2
T= 1.02

2. Nov 15, 2012

### Delphi51

Welcome to PF!
Looks good. I get a very slightly larger answer; might be worth running it through the calculator again.

3. Nov 15, 2012

### anaximenes

Your equations written as pie squared r instead of pie r squared, i think you did it right but it looks weird

4. Nov 15, 2012

### Lax0

its the equation in the text book. So can you explain how max tension gets minimum period?

5. Nov 15, 2012

### haruspex

Yes, the equation is correct, though it does look odd at first sight.
The stone has a certain distance to cover, 2πr, in one period. So minimum period means maximum speed, and that means maximum tension.

6. Nov 24, 2012

### anaximenes

Sorry your right, its so weird seeing pie digitally