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What are the x and y components of the velocity of the CM of the two bodies?

  1. Nov 16, 2009 #1
    1. The problem statement, all variables and given/known data

    Body A of mass 3 kg is moving int he x+ direction with a speed of 14 m/s. Body B of mass 4 kg is moving in the -y direction with a speed of 7 m/s. What are the x and y-components of the velocity of the CM of the two bodies?

    The answer is (6m/s,-4m/s).
    2. Relevant equations

    CMx=m1x1x+m2x2/m1+m2

    3. The attempt at a solution
    I am not getting the answer when I enter the figures into the equation. Is this the right equation? Please help it seems simple once I get the right equation.
     
  2. jcsd
  3. Nov 17, 2009 #2

    PhanthomJay

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    It seems from the solution that the 3Kg and 4kg blocks are reversed. Body A appears to be 4 kg, and Body B appears to be 3 kg.
     
  4. Nov 17, 2009 #3
    I'm still confused so if they are reversed can I ask what equation would I use to calculate x and y components?
     
  5. Nov 17, 2009 #4

    ehild

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    The coordinates of the CM in case of two bodies:

    [tex]x(CM)=\frac{x_1m_1+x_2m_2}{m_1+m_2}[/tex]

    [tex]y(CM)=\frac{y_1m_1+y_2m_2}{m_1+m_2}[/tex]

    The same holds for the components of velocity:

    [tex]V_x(CM)=\frac{v_{x1}m_1+v_{x2}m_2}{m_1+m_2}[/tex]

    [tex]V_y(CM)=\frac{v_{y1}m_1+v_{y2}m_2}{m_1+m_2}[/tex]

    ehild
     
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