Homework Help: Marathon runner velocity problem

1. Sep 4, 2010

Allura

1. Consider a marathon of 42.195 kilometers. In order to attain the qualifying time of 3 hours and 15 minutes to enter the race, a runner would need to run at an average velocity (in m/s) of

2. I thought this would be average speed = distance traveled/time interval spent traveling

3. Since they wanted it in terms of m/s, I divided 42.195 by 1000. Then to get seconds, I converted 3 hr and 15 mins to 11700 seconds, which gives 3.6E-6.

But apparently its wrong. Help?

2. Sep 4, 2010

iamalexalright

Re: Velocity...again

Why did you divide by 1000?

3. Sep 4, 2010

Allura

Re: Velocity...again

To go from kilometers to meters

4. Sep 4, 2010

iamalexalright

Re: Velocity...again

You are not canceling units correctly:

$$1 km * 1000 \frac{m}{km} = 1000 m$$

5. Sep 4, 2010

Allura

Re: Velocity...again

Ohhh, the right is answer is 3.6 then. Thanks! That makes more sense.