# Homework Help: Circular Motion

1. Feb 24, 2009

### liz777

1. The problem statement, all variables and given/known data
A ball has a radius of 2.25 m. What is the slowest speed of the ball at the bottom which will just make it around at the top of the path?

3. The attempt at a solution

I dont even know where to start with this problem. I dont understand it. Any help would be greatly appreciated!

2. Feb 24, 2009

### Tom Mattson

Staff Emeritus
Neither do I, because you didn't type in the entire problem statement. I'm guessing that the ball is tethered to a rope of radius 2.25 m, but that's just a guess. Please type in the problem statement exactly as it appears on your assignment.

3. Feb 24, 2009

### liz777

oh sorry...here it is:

When one spins a ball in a circular path which has a radius of 2.25 m, what is the slowest speed of the ball at the bottom which will just make it around at the top of the path?

4. Feb 24, 2009

### Tom Mattson

Staff Emeritus
You should begin by drawing a free body diagram of the ball at the top of its path. Then write down Newton's second law for the ball at that point. That's how you start all dynamics problems at this level.

5. Feb 24, 2009

### liz777

ok, I drew a diagram and I think I understand. Gravity pulls down on the ball, which is the acceleration so:
v^2=gr
=(9.8)(2.25)

Is this correct?

6. Feb 24, 2009

### Tom Mattson

Staff Emeritus
Right, just remember to take the square root. You found $v^2$, not $v$.

7. Feb 24, 2009

### liz777

ok, thank you! :) I understand it.