# Homework Help: Rotational motion problem

1. Jul 6, 2009

### balling12

1. The problem statement, all variables and given/known data
A car initially traveling at 25.9 m/s undergoes a constant negative acceleration of magnitude 2.10 m/s2 after its brakes are applied.
(a) How many revolutions does each tire make before the car comes to a stop, assuming the car does not skid and the tires have radii of 0.330 m? ... revs
(b) What is the angular speed of the wheels when the car has traveled half the total distance? .. rad/s

2. Relevant equations

3. The attempt at a solution
I used the kinematic equation to find the time it takes to come to a stop: 12.3 secs and the distance traveled: 305.67 m. I am unsure how to find the number of revolutions the tires make. However i worked out part B using the equation: W final^2=W initial^2+ 2(alpha)(Change in theta) and got the answer 19.1 rads but it is wrong.

2. Jul 6, 2009

### Staff: Mentor

Redo that last calculation. Hint: What's the average speed of the car as it comes to rest?
Hint: What's the circumference of the tires?

3. Jul 6, 2009

### balling12

Circumference is pie x diameter right?

4. Jul 6, 2009

Yes.