Homework Help: Runner A and Runner B

1. Sep 2, 2009

alexistheman

Runner A is initially 5.6 km west of a flagpole
and is running with a constant velocity of
8.7 km/h due east. Runner B is initially 4.2
km east of the flagpole and is running with a
constant velocity of 7.4 km/h due west.

How far are the runners from the flagpole
when their paths cross? Answer in units of
km.

How do i even start this, im stuck.

2. Sep 2, 2009

Jebus_Chris

Drawing the scenario is always a good place to start.
R1------------------------------F-------------------------R2
Now you're looking for when R1 and R2 pass each other. That means what?

3. Sep 2, 2009

alexistheman

displacement by chance?

4. Sep 2, 2009

alexistheman

Like i drew it out, but when i do i still dont know how to set it all up. Im so stumped. :(

5. Sep 2, 2009

alexistheman

I got .3 KM but it says its wrong.. ugh

6. Sep 2, 2009

Jebus_Chris

The runners will pass each other. This would happen after t hours. So that means that after t hours both runners will be at the same spot (not the same distance ran).
-Basically, at some time t, the two runners x position will be equal.

7. Sep 2, 2009

indep

8.7 km/h + 7.4 km/h = 4.7 km + 5.6 km

16.1 km/h = 9.8 km

t = 9.8 km / 16.1

t=.608695652

8.7 * .608695652 = 5.29565213

5.6 - 5.29565213 = .30434782

8. Sep 2, 2009

alexistheman

Hm, confusing. lol. I set it up and got 5.29 but ugh wouldnt it be .31

9. Sep 2, 2009

Jebus_Chris

Why don't you post what you did.

10. Sep 2, 2009

alexistheman

Ugh it wanted the full number, thanks ~.~

11. Sep 2, 2009

alexistheman

it was operator and stupid website error lol

12. Sep 2, 2009

indep

happens..i had trouble on this one early tonight but i figured it out..

13. Sep 2, 2009

alexistheman

well thanks man, heh.

14. Sep 2, 2009

no prob.