# Homework Help: Helpp me

1. Jan 16, 2005

### Alexs45

A 0.25-kg ball attached to a string is rotating in a horizontal circle of radius 0.5 m. If the ball revolves twice every second, what is the tension in the string?

2. Jan 16, 2005

### arildno

1) How can you figure out the velocity of the ball by the information given?
2) How is that velocity related to the centripetal acceleration experienced by the ball?
3) How is the centripetal acceleration of the ball related to the tension in the string?

3. Jan 16, 2005

### p53ud0 dr34m5

$$v = \frac{2 \pi r}{T}$$
$$a_c = \frac{v^2}{r^2}=\frac{4 \pi^2 r}{T^2}$$
$$m \cdot a_c = F_T + F_g$$
i dont know if thats it, because im kind of limited on my sources. im at work, and im not even supposed to be on this site. :rofl: the last equation is probably wrong, but i know the first two are right. well, i think.

Last edited: Jan 16, 2005
4. Jan 16, 2005

### Alexs45

i dont think that is right, i need the step by step help

5. Jan 16, 2005

### p53ud0 dr34m5

all you have to do is plug in the numbers.