# Homework Help: Which direction is the average acceleration going?

1. Oct 2, 2011

### iamjohnny56

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

An object moves along a circular path with a constant speed, |v|.

The average acceleration in going from A to B is
1. south
2. zero
3. west
4. north
5. east
6. none of the others

2. Relevant equations

a = Δv / Δt

tangential acceleration = mv^2 / r

3. The attempt at a solution

I'm not sure how to approach this question, but I think that the answer is east. A and B are perpendicular, and at the 45 degree line, the velocity would be pointing due east, so wouldn't the acceleration also?

Could someone point me in the starting direction/tell me what I'm missing?

2. Oct 2, 2011

### grzz

First of all theta only looks to be 45deg.
Second:
av acc = (vb - va)/t = [vb + (-va)]/t
Draw a diagram to find resultant of vb + (-va).

3. Oct 2, 2011

### DukeLuke

What you have here is actually the equation for the centripetal force (because mass is included). Remember F=ma, so the direction of this force will also be the direction of the centripetal acceleration (and if this is the only force acting on the object the direction of the total acceleration). http://en.wikipedia.org/wiki/Centripetal_force To find the average direction, maybe sketch the centripetal acceleration at a few different points symmetric across the center dotted line.