# Tangential acceleration

1. Feb 3, 2009

### elcaptain

1. The problem statement, all variables and given/known data
a ball of 2.5kg revolves in a circle on a string with a radius of 0.9m. at the moment when the string makes an angle of 60 degrees below the horizontal, the ball's speed is 7m/s. at this specific point, what is the tangential acceleration?

2. Relevant equations
A_t = r*angular acceleration
A_t = dv/dt

3. The attempt at a solution
I understand what tangential acceleration is and how to calculate it when a time interval is given. However, this scenario doesn't make much sense, and I can't find an equation to use that I could plug in some of my data. I know m*g*cos60 is the gravitational acceleration component that is tangent to the ball's circular rotation at that point in time, but that answer didn't work for tangential acceleration.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

Last edited: Feb 3, 2009
2. Feb 3, 2009

### Carid

Think in terms of forces.

3. Feb 3, 2009

### elcaptain

i understand there are forces, including centripetal force and gravitational force. but i do not understand how they directly relate to tangential acceleration.

4. Feb 3, 2009

### davieddy

I presume the circular motion is in a vertical plane.
Where the **** did you get cos(21) from?

5. Feb 3, 2009

### Carid

Suggest you do a drawing and consider which forces contribute to tangential acceleration and which don't.

6. Feb 4, 2009

### mplayer

Can you just use: a = v2/r

Or does it help in any way? I'm not sure where the mass and angle is coming into this if its rotating on a horizontal plane.