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Homework Help: Center of Mass of system of particles

  1. Feb 27, 2012 #1
    1. The problem statement, all variables and given/known data

    Four particles are in a 2-D plane with masses, x- and y- positions, and x- and y- velocities as given in the table below:

    M X Y Vx Vy

    1 8.9kg -2.6m -4.8m 3.2m/s -3.9m/s

    2 7.9kg -3.4m 3.6m -5m/s -5.2m/s

    3 9kg 4.7m -5.4m -6.3m/s 2m/s

    4 8kg 5.5m 2.7m 4.1m/s - 3.3m/s

    OK, so it first asks:
    What is the x position of the center of mass
    What is the y position of the center of mass

    I have answered these correctly as:
    CMx =1.07
    CMy =-1.22

    The next question asks:
    What is the speed of the center of mass:?

    I THOUGHT this would simply be sqrt[(CMx^2) + (CMy^2)] <-(the magnitude of CMy) which would be 1.622 m/s
    but this is INCORRECT. I have stared and re-read this question for an hour and simply cannot think of any other way to calculate.

    any thoughts would be greatly appreciated?
  2. jcsd
  3. Feb 27, 2012 #2
    after typing out the question, I may ahve already seen my error, I just calculated the magnitude of the distance from the origin, not its actual speed.. funny how asking the question makes you see things
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