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Homework Help: Two cars collide and fuse together

  1. Apr 8, 2014 #1
    1. The problem statement, all variables and given/known data

    Car= 25m/s on x axis and truck= 20m/s on y axis
    Car is 1250 kg truck is 1900kg
    They collide and fuse together and the combined wreckage slides of the road. With final velocity Vf and at angle ° with respect to x axis . there are no external forces acting for The duration of collision

    2. Relevant equations
    A) using conservation of momentum calculate the final velocity Vf and the angle° the instant after the impact one in x direction and one in y direction .

    B) show by a direct calculation of the kinetic energies just before and just after the collision that energy it's not conserved. What was the percent cubage in the kinetic energy? Where did the lost energy go?

    C) the fused wreckage slides a distance Delta(X) 150ft from the point of impact until it comes to rest use the work energy theorem to calculate the coefficient of friction Mk.

    Please someone solve it in support lost !
  2. jcsd
  3. Apr 8, 2014 #2


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    Gold Member

    You have a perfectly inelastic collision, conservation of energy doesn't work. use P_i = P_f or (m_i)(v_i)=(m_f)(v_f)

    take your system as the 2 cars.
    A. see above
    B. Why can't you use conservation of energy, not just here but in all inelastic collisions
    C. just use conservarion of energy: E_i +- W = E_f, use your final momentum from a to find initial energy, what does the work? and what is the final energy (choose the final stage when the wreckage is stopped)
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