# Homework Help: Help with acceleration

1. Dec 4, 2007

1. The problem statement, all variables and given/known data
A car traveling north at a speed of 40km/h turns right to head due east at a speed of 30km/h. This change in direction and speed takes 2.0 s. Calculate the average acceleration of the car.

2. Relevant equations
a = v-u/t

3. The attempt at a solution

Was wondering if you guys could help me with this question. I can find the magnitude quite easily however i cannot find the new direction. Would someone be able to post a detailed guide as to how to get the direction?

2. Dec 5, 2007

### Shooting Star

Write v and u using unit vectors i and j.

3. Dec 5, 2007

Sorry mate I'm kind of new to physics. Would you be able to give me some detailed working out (being annotated would help alot) as to how you come across the acceleration. I no im asking alot but its annoying me so much cause i wanna learn this before i progress and forget about it

4. Dec 5, 2007

### Shooting Star

Well, uhh...matey, all right.

Choose y-axis toward N and x-axis toward E.

u = 40j and v = 30i.

Average a = change in velocity/time = (v-u)/t = (30i - 40j)/2* 1000/3600 m/s (converting km/h to m/s). Simplify a bit.

You had said that you can find the magnitude quite easily. Still, the magnitude of ai+bj is sqrt(a^2+b^2).

Last edited: Dec 5, 2007