# Displacement around a 400m track

1. Sep 1, 2011

### bionut

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

A runner completes 6 1/2 laps around a 400m track during 12min reun test. What is the runners displacement at the end of the 12 min?

2. Relevant equations

3. The attempt at a solution

Well the distance covered is 2.6km or 2600m in 720s, avg speed = 3.61m/s

So I calculated the dispalcement to be: 200m, because he is 200m from his inital position, but the correct answer is 160m is anyone able to help?

2. Sep 1, 2011

### PeterO

Suppose the running track was actually a 100m square. If he started in one corner and finished in the opposite corner , he would be 141.2 m away.
If he started in the middle of one side, he would finish in the middle of the other side - a mere 100m away.
It would appear that on a standard running track, the 200m start is 160m displaced from the finish - back along the straight then around the bend.
I hope your problem gave sufficient detail of the track to get the definitive 160m answer.