# Homework Help: Collision and Conservation of Momentum

1. Oct 31, 2012

### maulucci

1. The problem statement, all variables and given/known data
Show that you can measure the magnitude of the velocity vectors which have units of distance/time with a ruler that measures distance, if a certain condition is met. What is this necessary condition.Use the Equation and Figure to prove below that this can be done.

2. Relevant equations
m1/m2=|v2a-v2b|/|v1a-v2b|

3. The attempt at a solution
would the condition be that the motion had to be linear meaning that both pucks have to have a straight path? if not could you point me in the right direction and im not sure how you would prove that using the above equation
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

File size:
9.4 KB
Views:
90
2. Nov 1, 2012

### Simon Bridge

I think it is asking about using only a ruler to get the velocity ... so you have to be able to measure some length and say "hey! I know what the speed was!". Just being linear is not going to work since you still need to time the object as well.

It looks like there is something missing from the question though - "show that you can measure the magnitude of the velocity vectors" of what?

3. Nov 1, 2012

### maulucci

ok so would a proof be showing that every vector is v=(Distance measure in meters)/(number of dots) with the direction

4. Nov 1, 2012

### haruspex

Clearly it is not possible to get the absolute velocities, so it must be asking for ratios of them.
It says to use the equation. Since the masses are unknown, the only use that can be made of the equation is to relate the ratio of the relative velocities in the x direction to that in the y direction:
|vx2a-vx2b|/|vx1a-vx2b| = |vy2a-vy2b|/|vy1a-vy2b|
Based on the diagram, we can eliminate some of the || operators.
But what to make of the 'dots'? It doesn't say they represent equal intervals of time, but they do look that way. They're closer after collision. But if we set that as the condition then the equation becomes redundant.
The question would make much more sense if it asked you to find the ratio of masses.

5. Nov 1, 2012

### Simon Bridge

I cannot tell because I don't know why you think your diagram has anything to do with the question. All you have actually told us is that it is your attempt at a solution.

It would help if you answered the following question:
Though:
... the "necessary condition" could be that the "dots" positions at equal time intervals.