Radial component of linear acceleration

[Hotsuma]

Homework Statement

A 66-cm-diameter wheel accelerates uniformly about its center from 120 rpm to 260 rpm rpm in 4.9 s.

Homework Equations

$a_t = r\alpha$
$a_c= r\omega^2$
$a= a_r+a_t$

The Attempt at a Solution

I have discovered that:
$\alpha = 3.0 \frac{rad}{s^2}$
and
$a_t = 0.99/frac{m}{s^2}$

I have tried using Pythagoras's theorem to solve for $a_r$, but that value does not work. What am I doing wrong?

 

[Hotsuma]

Oh, and I am using Mastering Physics and only have one submission left, so I had better make it count!

 

[Hotsuma]

Anyone have an idea for this one?

 

[LowlyPion]

Homework Statement

A 66-cm-diameter wheel accelerates uniformly about its center from 120 rpm to 260 rpm rpm in 4.9 s.

What is the question?

Have you considered the rotational analogues to linear kinematic motion?

http://hyperphysics.phy-astr.gsu.edu/hbase/mi.html#rlin

 

[Hotsuma]

it asks for the radial component of acceleration

 

[LowlyPion]

it asks for the radial component of acceleration

At what point?

a = ω²r

So that means it is simply ω dependent.

Are you sure they don't want α - angular acceleration?

 

[Hotsuma]

Well I've tried that and that value didn't work. The time limit is over I took a hit on that one. The answer they resulted in was 110 m/s. Whoa.