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Urgent Help Needed- Finding the speed at the centre of mass? Please help me

  1. Jan 4, 2010 #1
    Urgent Help Needed- Finding the speed at the centre of mass? Please help me :(

    Hi, I was attempting to work through this question.
    Anyways, I was working from a graph, so the radius 2.5 cm, the two of them collided, it was an inelastic collision as the two objects did part ways, so how do I find the centre of gravity?
    I attempted to calculate it... but if someone could help me out? The masses were 500g and 500g.

    So for x and y, would I do:
    Xcg = (500)(0.025) + (500)(1.5)(0.025) / 1000 ?
    Ycg = (500)(0.025) + (500)(0.025) / 100 ?

    That's what I was thinking but I'm not entirely sure.

    After this, I also have to find the momentum of the centre of gravity... so for that, I need the masses and the speed.

    Even though the objects didn't stick together, would I add the masses when solving for the momentum at the centre of mass?

    I was reading on the internet and it said: "The center of mass velocity of a system of particles is the average velocity of all the particles weighted relative to their mass"

    but what I'm confused about is, do I add all the velocities... like the velocities of both the masses before and after the collision? So I'd have 4 velocities? But I'd only add the masses twice right? So it would be the velocities / 1000 g

    Could someone really help me. Please.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Jan 5, 2010 #2

    vela

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    Re: Urgent Help Needed- Finding the speed at the centre of mass? Please help me :(

    I answered your question in the other thread, but let me elaborate.

    When you calculate the velocity of the center of mass, you're calculating it for a certain point in time, and the velocities that enter into the formula are those of the objects at that point in time.
     
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