# Direction of angular acceleration

1. Feb 6, 2008

### brendan3eb

1. The problem statement, all variables and given/known data
Imagine a car driving on the XY plane in the +y-direction. If it is slowing down, in what direction is the angular acceleration of the wheels?

(a) the +x-direction
(b) the -x-direction
(c) the +y-direction
(d) the -y-direction
(e) the +z-direction

2. Relevant equations
a=αR

3. The attempt at a solution
I am just really lost when it comes to this problem. The apparent answer is A, but I do not understand why. I can't conceptualize angular acceleration with the axes..

The solution says the wheels have an angular velocity in the -x-direction and thus since the angular velocity is decreased the acceleration would be in the +x-direction. I get the second step, but I don't understand how you determine the angular velocity is in the -x-direction

Last edited: Feb 6, 2008
2. Feb 6, 2008

### brendan3eb

Actually, I think I get it now after messing around with some pictures..still, I think this was a stupid and poorly phrased problem.

3. Feb 7, 2008

### physixguru

think it as applying a force to stop the wheels....