# Angular acceleration?

#### Nanabit

A rotating wheel requires 2.93 s to complete 37.0 revolutions. Its angular speed at the end of the 2.93 s interval is 97.1 rad/s. What is the constant angular acceleration of the wheel?

I know this should be easy. I'm just missing something. I figured 37 rev = 232 rad (=theta). Then I used the kinematic
Theta(f) = Theta(i)+(omega)(i)t+(1/2)(alpha)(t^2). But somehow it isn't working out. I know the answer should be around 15 or so but I keep getting 120 rad/sec^2!!

#### jamesrc

Gold Member
You can't use your initial equation directly because you don't know the initial velocity yet. Use &omega;f = (&omega;i) + &alpha;*t; to find &omega;i. Then you can plug that in to your other constant acceleration question to find &alpha;. If I did it correctly, the acceleration should come out closer to 10 rad/s

#### Nanabit

How can you use ùf = (ùi) + á*t to find ùi when you don't know what á is?

(alright well you know what those symbols should mean)

#### jamesrc

Gold Member
You solve for &omega;i in terms of &alpha; and plug it into the other equation. It's a system of 2 equations with 2 unknowns.

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