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Vehicle Momentum Question

  1. Nov 6, 2008 #1
    1. The problem statement, all variables and given/known data

    The diagram below shows a skethc drawn by an accident investigator following a head-on collision between two vehicles.

    Direction of Travel A (speed 12.5 m/s) and 2400kg -------------> <---------------- Direction of Travel of B, 3600kg, unknown velocity.

    Final Position of vehicles:

    The diagram shows two boxes, repsenting the vehicles, attached together. One box is A, and is 2400 kg. The second is 3600 kg. Also, is X (where the vehicles collided) and an arrow to the left with 8.4m, which is the distance the vehicles travelled.

    The Question: Determine the speed of the interlocked vehicles immediately after impact.

    The second question: Vehicle A was known to be moving at 12.5m/s just before the impact. Calculate the speed of vehicle B just before impact.

    2. Relevant equations

    Right, for the first question I assume the equation Kinetic Energy = 1/2 mv^2 is relevant. The answer is a combined speed of 4.6 m/s but unfortunately, there is little point in me knowing the answer unless I can figure out how to get there.

    For the second question, I am clueless what sort of equation would be used. However, I know the answer is 16 m/s.

    3. The attempt at a solution

    For the first question, I tried to do Kinetic Energy = 1/2 mv^2 = 1/2 mv^2 to say that the total energy when the two vehicles collide is the same and rearrange it to find the second velocity. But in retrospect, that seems to be going down the wrong avenue?

    Other than that, I can't figure out what else to use or try.

    I'd appreciate anyone who can shed some insight or help. If you don't understand the question, I'll elaborate as best I can.

  2. jcsd
  3. Nov 7, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper

    Hi mandos! :smile:

    Yes, this is a totally inelastic collision, so KE isn't conserved.

    What is the whole question? :confused:

    There isn't enough information to solve this.
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