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Homework Help: Something Simple

  1. Jun 29, 2007 #1
    1. The problem statement, all variables and given/known data

    2 cars collide going 50 mph each.

    The closing velocity is 100mph

    Barring the fact that in the real world no accident is perfectly equal, do both drivers experience 50mph of deceleration each, or 100mph of deceleration each?

    My guess is since they both decelerate in the same distance and in the same time as(for example) 1 car hitting an wall that there is 100mph of G-forces being applied, but that since there are 2 drivers it is shared equally. Thus 50 mph

    Thank You
  2. jcsd
  3. Jun 29, 2007 #2


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    Each driver goes from 50 mph (relative to the pavement) to 0 mph relative to the pavement and so experiences a deceleration ot 50 mph divided by the time involved.
  4. Jun 29, 2007 #3
    Thanks for the help, -but- (while keeping in mind that I am a product of the public educational system)

    You didnt answer my question completely

    Maybe I can clarify, I need to be assisted with this problem, not for homework, but because several of my older friends insist that there is 100 mph worth of deceleration energy that is experienced each, per driver.

    (We entered into the discussion while talking about seat belts)

    So am i right? or am I wrong? do the drivers experience 50mph worth of deceleration each? or 100 each.

    You bolded "divided by the time involved" and I think that you are saying that I am indeed wrong because i am not factoring in the speed at which they travel.

    Thank you for your patience.
  5. Jun 29, 2007 #4
    If by "50 mph worth of deceleration" you mean that each of the cars decelerates from 50 mph to 0 mph, then you are correct (assuming the cars have equal mass, and all that). It's like slamming a car into a wall at 50 mph, only symmetrical.

    So although the relative speed of each of the cars with respect to the other car is initially 100 mph, each of them only 'needs' to reduce its speed by 50 mph in order to get to a standstill, which is basically what happens in such a collision.
  6. Jun 29, 2007 #5
    Thank you.

    Is there any counter points that may have been overlooked? anyone else have anything to add to this?

    Thanks in advance
  7. Jul 1, 2007 #6


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    In accordance with HallsofIvy's response, if you believe your answer is correct, you must convince yourself that Car A's 50mph change in speed in the head on '100 mph close speed' collision occurs over the same time period as in the case when car A is travelling at 50 mph and rams a stationary wall. Clearly the car goes from 50 to 0 in either case, but is the deceleration the same??
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