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Homework Help: 2d Collisions

  1. Jul 20, 2015 #1
    1. The problem statement, all variables and given/known data

    A car with a mass of 1400 kg is westbound at 50 km/h. It collides at an intersection with a northbound truck having a mass of 2000 kg and travelling at 40 km/h. What is the initial common velocity of the car and truck immediately after the collision if they have an inelastic collision? For this question, a diagram is drawn for you. The mass' stick after colliding

    2. Relevant equations

    3. The attempt at a solution
    So i tried 2 different methods
    m1v1+m2v2=mv* and the other method i used was that i drew a triangle (made vectors) found the hypotenuse (momentum combined) and from there i divided by the mass to get the velocity.
    When i did this i got 2 different answers im really confused which one is correct please help :)
  2. jcsd
  3. Jul 20, 2015 #2
    Momentum is a vector and so you need to pay attention to the directions .

    The best and easiest way to solve this question would be to conserve momentum along north-south direction , and then along east west , and then simply find the net magnitude of velocity .

    I cannot understand what exactly you have written , but from what I can tell , method 2 seems to be correct .
  4. Jul 20, 2015 #3
    Both methods are correct. The second method is just a graphical representation of the first.
    But as Qwertywerty said: you can't just add vectors.
  5. Jul 20, 2015 #4
    Oh, okay thank you soo much guys I get it now :)
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