# Constant acceleration problem

1. Jan 3, 2006

### kylera

Bloody textbooks and their odd answers...

I've tried to solve this problem, and I've solved through it, only to realize that my answer and the book answer are drastically different. A keen eye in the process would be most appreciated.

Question: A runner hopes to complete the 10000-meter run in less than 30.0 minutes. After 27.0 minutes, there are still 1100 meters to go. The runner must then accelerate at 0.20 m/s^2 for how many seconds in order to achieve the desired time?

My solution:
Initial velocity = the rate at which the previous 8900 meters was covered in 27.0 minutes = 8900/27.0 = 3.29e2 m/s
Final velocity = the rate at which the last 1100 meters must be covered in the last 3.0 minutes = 1100/3.0 = 3.7e2 m/s

I then used the 'final velocity' = 'initial velocity' + 'time' * 'acceleration' equation, and got what I thought was, and turned out to be, an absurd value for 'time' = 200(!) seconds. The book says '3.1 seconds'. Can anyone see my mistake here so far, or what I should've or should not have done? Much thanks.

2. Jan 3, 2006

### andrewchang

your initial velocity is not in m/s- when you divided it, you got 329 m/minutes.

3. Jan 3, 2006

D'oh!!!

Thanks!