Collision between falling body and body shot upwards

1. Sep 1, 2009

jasper619

Hi this is my first post thanks to who ever contributes!

1. The problem statement, all variables and given/known data
A man drops a ball from the top of a 22m building. At the same instant his friend below throws a ball upwards at 22 m/s. What distance from the ground do the two balls meet.

Ball A
-------
v1 = 0 m/s
a = 9.8m/s down
t=?
d=?

Ball B
--------
v1 = 22 m/s up
a = 9.8 m/s down
t = ?
d = ?

This assumes that ball A was dropped right at 22m and the other ball was thrown from ground level. Air resistance is negligible.

My attempts have all failed my general approach was to solve for time that they hit at and then use that to find the distance one of the balls traveled. We are to use basic equations relevant to kinematics, force or energy (no calculus related stuff). Any help would be much appreciated

Jasper

2. Sep 1, 2009

Hootenanny

Staff Emeritus
Welcome to Physics Forums.

HINT: In terms of the balls' displacement, what does a 'collision' mean?

3. Sep 1, 2009

jasper619

well wouldn't a collision be when the displacements overlap?

4. Sep 1, 2009

Hootenanny

Staff Emeritus
If the balls collide at a height d0 above the ground, then the displacement of ball B is d=d0. What is the displacement of ball B?

5. Sep 1, 2009

jasper619

If you meant what is the displacement of ball a then it is d = 22 - d0 right?

hmm wait I think i know what to do now I will post my result

6. Sep 1, 2009

Hootenanny

Staff Emeritus
Indeed I did and that is correct.

7. Sep 1, 2009

jasper619

I dont know what to do with time as all my formulas ask for it any tips would be nice

8. Sep 2, 2009

Hootenanny

Staff Emeritus
My hint is pretty much the same as for the displacement: the balls must collide at the same time. You should be able to write down two equations, one force each ball. Each equation should have two unknowns - time and displacement (don't forget to use the previous hint for displacement). Now, you have two equations with two unknowns - how would you usually go about solving this type of problem?

9. Sep 2, 2009

jasper619

Ya i figured it out thanks alot