# What is the tangential acceleration?

## Homework Statement

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?

## Homework Equations

A_t = r*angular acceleration
A_t = dv/dt

## 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.

## The Attempt at a Solution

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Think in terms of forces.

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

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

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

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.