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Impulse exerted on car during collision

  1. Jul 26, 2015 #1
    1. The problem statement, all variables and given/known data
    Two cars are approaching a perpendicular intersection without a stop sign. Car 1 has a mass m1=900kg and is heading north at v1=25m/s. Car 2 has mass m2=700kg and is heading west at an unknown speed v2. The two cars collide at the intersection, and stick together as a result of the collision. The police report stated that after the collision, the two cars moved together in a direction 40∘ west of north and stopped after sliding d=35m from the collision point.

    What is the magnitude of the impulse exerted on car 1 during the collision?

    What is the magnitude of the impulse exerted on car 2 during the collision?

    2. Relevant equations
    x(t) = x_o+v_o*t+1/2*a*t^2
    mv = m1v_1'+m2v_2'
    J = mv_f - mv_o

    3. The attempt at a solution
    Velocity of car 2:
    26.9711 m/s

    Velocity after collision:
    18.35729 m/s

    Momentum of car 1 before collision: 22500 kg m/s

    Momentum after collision: 1600 kg * 18.35729 = 29371.664 kg m/s

    sqrt((29371.664)^2 - (22500)^2) = 18879.7
    (which is equal to the momentum of car 2)

    If I can figure out the first one I can do the second one I just need to know what I'm doing wrong.
     
  2. jcsd
  3. Jul 26, 2015 #2

    BvU

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    In PF you want to show what you did to get these numbers...
    I can follow this one, but generally it's impossible to find what goes wrong where ...

    Yes, but what is the momentum of car 1 after the collision ?
    And then you want to make a drawing to see what the change of momentum for car 1 is.
     
  4. Jul 26, 2015 #3
    Would that be 18.35729*900 = 16521.6? Because 16521.6^2-22500^2 is a negative. Should I just use 16521.6sin40 = 10619.9?
     
  5. Jul 26, 2015 #4
    thats velocity after collision*mass of car 1*sin(theta)
     
  6. Jul 27, 2015 #5

    BvU

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    What does the drawing tell you ? Do you realize that momentum is a vector ? It has two components !
     
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