# Homework Help: Rotational Motion (should be easy-need quick tip)

1. Oct 7, 2008

### mistymoon_38

1. The problem statement, all variables and given/known data

A car starts from rest and moves around a circular, horizontal, level track of radius 30 m. Its speed increases at the constant rate of 0.5 m/s^2. (a) What is the magnitude of the net acceleration 15 s later? (b) What angle does the net acceleration make with the car's velocity at this time?

2. Relevant equations

3. The attempt at a solution
I think I got part A. I just found the vector sum of of the centripetal accleration, V^2/R (found V by taking integral of 0.5 from 0-15s), and the given tangental accereration of 0.5.
Does this sound right?
As for part B I have no idea. I dont think I can use constant acceleration kinematic equations...

Also- is there a difference between the angular acceleration and the net acceleration?

2. Oct 8, 2008

### Kurdt

Staff Emeritus
For B you know the components of the acceleration. All you need to do is find the angle between the tangential acceleration and the resultant or net acceleration.

Yes angular acceleration is different to the net acceleration. This page may be of use to you.

http://hyperphysics.phy-astr.gsu.edu/HBASE/rotq.html#drot

3. Oct 8, 2008

### mistymoon_38

thanks i think i got it now.