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Ineleastic perpendicular collision question

  1. Apr 23, 2017 #1
    1. The problem statement, all variables and given/known data
    Car 1: 2200kg
    Initial direction: South
    Car 2: 1800kg
    Initial direction: East
    Cars lock together and slide 11.25M (S 22.25 E)
    At an acceleration that is 9.81 m (back) (it's a coincidence that this is gravity.)
    2. Relevant equations
    Who's fault was the collision if the speed limit was 50km/h?

    I can't find momentum without a velocity so I'm very lost

    3. The attempt at a solution
     
  2. jcsd
  3. Apr 23, 2017 #2

    haruspex

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    Just invent variables to represent the three unknown velocities, the two before and the one after collision.
    Momentum gives you two equations, stopping distance gives you a third.
     
  4. Apr 23, 2017 #3
    Which equations are those? We only got one equation for in elastic in class, what about the distance one too? What you said makes sense but I can't find 3 equations
     
  5. Apr 23, 2017 #4

    gneill

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    Hi MomentumIsHard,

    You need to make some attempt before help can be given. What details about the motion after the collision do you know?
     
  6. Apr 23, 2017 #5
    All the question states is that it moves 11.25 M [Back] (even though other directions were given in terms of east and south) at an acceleration of 9.81 m/s. The problem is I don't know where to start so I can't really make an attempt. Once I get one momentum I could pretty easily figure this out but I can't quite figure that out with no velocities given
     
  7. Apr 23, 2017 #6

    haruspex

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    Conservation of momentum (one for each of two dimensions) and the SUVAT equation relating speeds, distance and (constant) acceleration.
     
  8. Apr 23, 2017 #7

    gneill

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    No idea what "[Back]" is supposed to mean, but it doesn't matter if you're given the rest of the motion details. You have a distance, an acceleration, and a final speed. What can you deduce from that?
     
  9. Apr 23, 2017 #8

    haruspex

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    I think it means the direction of the given acceleration is opposite to the motion.
     
  10. Apr 23, 2017 #9

    gneill

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    That's quite likely. Of course deceleration is also implied by the fact that the combined mass travels a limited distance.
     
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