# Homework Help: Calc. the car's average acceleration

1. Sep 5, 2007

### hullio

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

A Car with a velocity of 25m/s[E] changes its velocity to 25m/s in 15s. Calc. the car's average acceleration.

2. Relevant equations

Aav= Vf - Vi / T

3. The attempt at a solution

I know that the angle is = to 45 degrees S of W since it's a right angle triangle and two sides are equal, therefore, 90 + 45 + 45 = 180.

2. Sep 5, 2007

You are dealing with vectors here? Do you know how to express the formula you gave with vectors?

3. Sep 5, 2007

### hullio

Yes dealing with vectors. Express the formula with vectors? I don't think so...? I've been learning all this Dx and Dy stuff in class. X-components, y-compenents, sin/cos/tan stuff.

4. Sep 5, 2007

### Lemm

Well X and Y components are the axis, or directions North is +Y, South is -Y, East is +X, West -X.

Just start by making a quick outline of the problem, on a set of axis, that always helps.

5. Sep 5, 2007

### learningphysics

Are you familiar with this type of notation: $$\vec{r} = 34\vec{i} + 25\vec{j}$$ (just an arbitrary vector... nothing to do with the problem... i denotes a unit vector in the x-direction... j denotes a unit vector in the y direction)