Calculating the constant acceleration

[thushanthan]

Homework Statement

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?

Homework Equations

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 x_i=0 and V_xAvg 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 x_i =0 ) then I am getting the correct answer which is 12m/s².

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

Thank you!

 

[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.

 

[thushanthan]

Thank you