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Elastic collision.

  1. Nov 23, 2008 #1
    1. The problem statement, all variables and given/known data


    A 70kg man who is ice skating north collides with a 30kg boy who is ice skating west. Immediately after the collision, the man and boy are observed to be moving together with a velocity of 2m/s in a direction 37 degrees north of west. What was the magnitude of the boy's velocity before collision.
    2. Relevant equations



    3. The attempt at a solution
    I do not really know where to start. Could someone please list equations that are needed for this problem.
     
  2. jcsd
  3. Nov 23, 2008 #2
    i meant to title inelastic
     
  4. Nov 23, 2008 #3
    use conservation of momentum, you should have an equation for the y axis (north/south) and an equation for the x axis (east/west)
     
  5. Nov 23, 2008 #4
    I do not see how to use it when only the final velocity is given.
     
  6. Nov 23, 2008 #5
    ok im not sure if this is right, but i made the equation m2v2cos=m1v1'cos+m2v2'cos
    and found v2 to equal 2.13 would that be my final answer?
     
  7. Nov 23, 2008 #6
    usually good to break these down into momentum in x direction and y direction

    [itex]
    M_{man}V_{man} \hat{y} = M_{final}V_{yfinal} \hat{y}
    [/itex]
    [itex]
    M_{boy}V_{boy} \hat{x}=M_{final}V_{xfinal} \hat{x}
    [/itex]
    [itex]
    M_{final} = M_{boy} + M_{man}
    [/itex]
    [itex]
    V_{yfinal} = \left( 2 \frac{m}{s} \right) cos(37^{\circ})
    [/itex]
    see if you can determine the other final V and solve, lemme know if you have questions on notation and such
     
    Last edited: Nov 23, 2008
  8. Nov 23, 2008 #7
    Thanks im good now
     
  9. Nov 23, 2008 #8
    xcellent,

    "may entropy increase in a way that favors your sword"
    -Logicaltime
     
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