# Plug in time to find the acceleration

Heres the problem Im working on...

http://img502.imageshack.us/img502/1613/rotut5.jpg [Broken]

Im trying to figure how to plug in time to find the acceleration....

I found the first acceleration of 100mm/s^2......but im not sure how to get the others...

I was using the formula

$$a_{t} = r\theta$$

$$a_{n} = r\omega^2$$

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## Answers and Replies

Doc Al
Mentor
I was using the formula

$$a_{t} = r\theta$$

$$a_{n} = r\omega^2$$
That first equation should be:

$$a_{t} = r\alpha$$

How can you find the angular speed at each of those times?

at time = 0 I was able to do

$$a_{t} = r\omega = 9(.200)(.5) = .100 = 100mm/s^2$$

and that is correct for the first answer....

but for the other times I wasnt sure...

ok I figured it out for time at 2...and its the same for each time....its just

$$a_{t} = r\alpha = (.200)(.5) = .100$$

$$\omega = \omega_{o} + \alpha(t)$$

$$\omega = .5 rad/s$$

$$a_{n} = r\omega^2 = (.200)(.5)^2 = .050$$

$$A = \sqrt{a_{t}^2+a_{n}^2} = 111.8 mm/s^2$$