# Homework Help: Instantaneous V Problem

1. Sep 26, 2004

### Warwick

Hello, I was doing the chapter review and a few problems gave me trouble. I forgot this is the wrong forum, err, please move it, im sorry.

1.) Runner A is initially 4.0 mi west of a flagpole and is running with a constant velocity of 6.0 mi/h due east. Runner B is initially 3.0 mi east of the flagpole and is running with a constant velocity of 5.0 mi/h due west. How far are the runners from the flagpole when they meet.

2.)A tortoise can run with a speed of .10m/s and a hare can run 20 times as fast. In a race, they both start at the same time, but the hair stops to rest for 2.0 mintures. The tortoise wins by 20 cm. a. How long does the race take? b. What is the length of the race?

I'm sure i'll have more by the end of tonight . If you can work these out, I would really appreciate it. Thanks!

Last edited: Sep 26, 2004
2. Oct 19, 2004

### Martin Cook

Hi.

The key in both problems is to consider differenct reference frames, i.e. change what point of view you look at the problem from. For example in the first one, one is running east at 6mi/h, and the other west at 5mi/h. If you look at it from the first person's point of view though, he (or she) sees the other person coming closer at the combined speed of 11mi/h. You can then work out times and distances and stuff.

The second one is a bit more complicated, but uses the same principle. It doesn't matter when the hare rests, as it takes the same amount of time wherever it happens. Let's say it rest at the start for convenience. Work out how far away they are from each other when the hare starts running. Then work out how fast the one is relative to the other, and then get times.