# Ball Collision need help please.

1. Oct 8, 2007

### physics2004

1. The problem statement, all variables and given/known data

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.

picture attached
2. Relevant equations
1. When and where do B1 and B2 collide?

3. The attempt at a solution

none can't start...

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2. Oct 8, 2007

### 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?

3. Oct 8, 2007

### physics2004

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

Last edited: Oct 8, 2007
4. Oct 8, 2007

### 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).