# Homework Help: Rolling as Translation and Rotation Combined

1. Oct 21, 2009

### G-reg

1. The problem statement, all variables and given/known data
An automobile traveling at 30.0 km/h has tires of 85.0 cm diameter.

(b) If the car is brought to a stop uniformly in 15.0 complete turns of the tires (without skidding), what is the magnitude of the angular acceleration of the wheels?

(In part a I found the angular speed to be 19.6 rad/s

2. Relevant equations

(w^2 - wi^2)/(2 * change in theta) ??

3. The attempt at a solution

-wi^2/(2 *(2* 15pi) = angular acceleration

I'm super lost and would appreciate any help at all. I just need a pointer in the right direction!

2. Oct 22, 2009

### rl.bhat

Your formula is correct. Check your ωi.

3. Oct 22, 2009

### G-reg

I know that my wi is correct though..
Is there another way to solve this problem maybe?

4. Oct 22, 2009

### G-reg

Well, would the answer 2.038rad/s^2 make sense?
Because that's what I got for my answer but I wasn't expecting the acceleration to be that much slower than the speed

5. Oct 22, 2009

### rl.bhat

6. Oct 22, 2009

### G-reg

Ok thank you so much!