# Homework Help: Calculating the constant acceleration

1. Sep 29, 2010

### thushanthan

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

An automobile moving along a straight track changes its velocity from 40 m/s to 80 m/s in a distance of 200 m. What is the (constant) acceleration component of the vehicle during this time?

2. Relevant equations

3. The attempt at a solution

I try to solve this problems with 2 different approaches.

First :

Since we don't know the time (t) , we need to calculate the time. If we assume the initial position as xi=0 and VxAvg as 40 m/s , then I am getting t=5 sec. But that doesn't help me to reach the final answer. I ended up with 8.0m/s2.

Second:

If I didn't care about the time(t) and if I use Velocity as a function of position eq ( assuming xi =0 ) then I am getting the correct answer which is 12m/s2.

My question is "Can I assume the initial position is xi=0? IS IT CORRECT?"

Thank you!!

2. Sep 29, 2010

### p21bass

Your second method is correct. We don't need the time for this problem, as we can use the constant acceleration equation that relates initial velocity, acceleration, initial location, and final location to final velocity.

3. Sep 29, 2010

Thank you