# Relative Motion Question

1. Oct 16, 2010

### PhysicsGenius

1. The problem statement, all variables and given/known data
I am given the location of 3 points in space:
Z1= 3+3i
Z2= 7+5i
Z3= 5+5i

and the velocity of two points:
V_1= 8+0i
V_2= 7+6i

How do I find V3?

2. Relevant equations
V_1/2= V_1-V_2
V_3= V1+V_3/1
V_2/1= V_2-V_1

3. The attempt at a solution

I have the equations, but I just can't seem to figure out how to relate V_3 with V_2 and V_1. Can anyone help?

2. Oct 17, 2010

### tiny-tim

Hi PhysicsGenius!

(try using the X2 icon just above the Reply box )

I don't understand …

V3 could be anything

what is the complete question? ​

3. Oct 17, 2010

### TheJCBand

Yeah, it looks like you're missing at least one piece of information about Z3.

4. Oct 17, 2010

### PhysicsGenius

that is the entire problem, it also states that the 3 points are all on the same link, if that helps

Last edited: Oct 18, 2010
5. Oct 18, 2010

### tiny-tim

(just got up :zzz: …)
Do you mean the same line?

But that's obviously not true (unless, say, Z2 should have been 7 + 7i).

6. Oct 18, 2010

### TheJCBand

Being on the same link means that the distances between these points is fixed. This gives you two more independent equations:

(x1 - x2)2 + (y1 - y2)2 = (some constant),
(x1 - x3)2 + (y1 - y3)2 = (some other constant).

7. Oct 18, 2010

### tiny-tim

You mean that Z1 Z2 and Z3 are three points on a rigid body?

But then (Z1 - Z2) should be perpendicular to (V1 - V2), which it isn't

8. Oct 18, 2010

### nvn

Last edited by a moderator: Apr 25, 2017
9. Oct 18, 2010

### nvn

OK, I think I have figured out why this problem has baffled everyone, so far. It is a bogus problem. PhysicsGenius made up those numbers listed in post 1, pretending it is the given problem statement. PhysicsGenius is seemingly currently unaware that you cannot just arbitrarily type numbers. The numbers in post 1 are physically impossible.

PhysicsGenius: Please post the exact, full wording of the given problem statement. And proofread it carefully to ensure there are no typos. Also, please post any diagram, if it has one. I think we will be able to help you, if you do this.