How to Calculate Relative Motion with Given Positions and Velocities?

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Discussion Overview

The discussion revolves around a homework problem involving the calculation of relative motion given the positions and velocities of three points in space. Participants are attempting to determine how to find the velocity of the third point based on the provided information.

Discussion Character

  • Homework-related
  • Debate/contested

Main Points Raised

  • PhysicsGenius presents a problem with three points in space and two known velocities, seeking help to find the velocity of the third point.
  • Some participants express confusion about the completeness of the problem, noting that V3 could be anything without additional information.
  • There is a suggestion that the three points are on the same link, which some participants interpret as meaning they are on a rigid body, but this leads to further confusion regarding the relationships between the points and their velocities.
  • One participant proposes that being on the same link implies fixed distances between the points, suggesting additional equations could be derived from this assumption.
  • Another participant challenges the validity of the problem, stating that the numbers provided appear physically impossible and requesting clarification on the problem statement.

Areas of Agreement / Disagreement

Participants generally agree that the problem lacks sufficient information and clarity, leading to multiple competing interpretations and unresolved confusion about the physical validity of the scenario.

Contextual Notes

Limitations include potential typos in the problem statement, ambiguity regarding the term "link," and the need for additional context or diagrams to clarify the relationships between the points and their velocities.

PhysicsGenius
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Homework Statement


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?

Homework Equations


V_1/2= V_1-V_2
V_3= V1+V_3/1
V_2/1= V_2-V_1

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?
 
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Hi PhysicsGenius! :smile:

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

I don't understand …

V3 could be anything :confused:

what is the complete question?​
 
Yeah, it looks like you're missing at least one piece of information about Z3.
 
that is the entire problem, it also states that the 3 points are all on the same link, if that helps
 
Last edited:
(just got up :zzz: …)
PhysicsGenius said:
that is the entire problem, it also states that the 3 points are all on the same link, if that helps

Do you mean the same line?

But that's obviously not true (unless, say, Z2 should have been 7 + 7i). :confused:
 
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).
 
PhysicsGenius said:
that is the entire problem, it also states that the 3 points are all on the same link, if that helps

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 :confused:
PhysicsGenius said:
Z1= 3+3i
Z2= 7+5i
Z3= 5+5i

V_1= 8+0i
V_2= 7+6i
 
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.
 

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