1. Standard memberCrowley
    Not Aleister
    Control room
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    27 Sep '05 14:012 edits
    Hi guys, I need to do a calculation, but I can't find anything on the web to help me out.

    Check this: http://www.redhotpawn.com/board/showthread.php?threadid=30250
  2. Standard memberPBE6
    Bananarama
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    27 Sep '05 17:501 edit
    Originally posted by Crowley
    Hi guys, I need to do a calculation, but I can't find anything on the web to help me out.

    Check this: http://www.redhotpawn.com/board/showthread.php?threadid=30250
    Sounds like you need a few equations:

    1. Conservation of momentum:

    m1*v1 + m2*v2 = m1*u1 + m2*u2

    Where: m1, m2 are the masses of the objects; v1, v2 are the velocities before the collision; and u1, u2 are the velocities after the collision; and

    2. Momentum/energy relation for an elastic collision:

    0.5*m*(v^2) = dp/dt

    Where: m is the mass of the object, v is the velocity, and dp/dt is the change in momentum over time.

    What is the question exactly?
  3. SubscriberAThousandYoung
    All My Soldiers...
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    27 Sep '05 20:231 edit
    Originally posted by Crowley
    Hi guys, I need to do a calculation, but I can't find anything on the web to help me out.

    Check this: http://www.redhotpawn.com/board/showthread.php?threadid=30250
    OK. It was accident.
    A motorbike hit a pedestrian, I want to know how fast the bastard was going.

    I have the weight of the pedestrian and the bike and I have the displacement of the pedestrian.

    What formula can I use?


    http://www.redhotpawn.com/board/showthread.php?threadid=30250

    The kinds of collision problems that are dealt with in low level physics are perfectly inelastic and elastic collisions. Your example is neither; it's an inelastic collision, but not perfectly inelastic. You need to know that kinetic energy is not conserved. However unlike a perfectly inelastic collision, the two bodies do not stick together and act like one body.

    What you do know is that momentum is conserved. So, if you determine what the momentum of the pedestrian was, and you know the mass of the motorcycle and the rider including gas in the tank, you can figure out the velocity of the motorcycle. How would you do that though?

    If you can determine the distance the person skidded on the concrete and the coefficient of friction between person and concrete, I think you can determine how fast the person was going when they hit.

    It's a pretty complex problem and more information is needed to solve it.
  4. Standard memberRagnorak
    For RHP addons...
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    27 Sep '05 23:48
    Originally posted by Crowley
    Hi guys, I need to do a calculation, but I can't find anything on the web to help me out.

    Check this: http://www.redhotpawn.com/board/showthread.php?threadid=30250
    Can you not just go out and measure the length of the skid marks, assuming that driver braked?

    D
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