When and where do two balls collide if one is thrown horizontally and one drops?

[physics2004]

Homework Statement

Ball 1 (B1) and Ball 2 (B2) are located at (x,y)=(0,0) and (x,y)=(d,h).
At t=0, B1 is sent towards the initial location of B2 with a speed vi. At the same
instant that B1 is launched, B2 falls towards the ground with zero initial velocity.
Assume there is no air resistance.


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Homework Equations

1. When and where do B1 and B2 collide?

The Attempt at a Solution

none can't start...

 

[Mindscrape]

You will want to figure out the when part before the where part. When does B2 hit the ground? What is the condition for B1 to hit B2 then?

 

[physics2004]

im pretty sure the question is asking when will they hit in the air not after b2 lands

 

[Timo]

- There is no ground level given (the natural assumption that h=0 was ground level is arbitrary). Don't worry about that for now, you can rethink the case h<0 later.
- The condition for the two balls to meet is having the same position at the same time (for arbitrarily small balls, at least).

As a sidenote unrelated to the question but possibly interesting: The problem is a nice example of one of the ideas that led to the general theory of relativity; I might comment on that later if you're interested (after the problem at hand is solved).