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    alra's Avatar
    alra Posts: 2, Reputation: 1
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    #1

    Nov 20, 2007, 02:41 PM
    Car Collision (Conservation of Energy)
    The front 1.20 m of a 1500 kg car is designed as a "crumple zone" that collapses to absorb the shock of a collision.

    (a) If a car traveling 22.0 m/s stops uniformly in 1.20 m, how long does the collision last?

    (b) What is the magnitude of the average force on the car?

    (c) What is the acceleration of the car? Express the acceleration as a multiple of the acceleration of gravity.
    terryg752's Avatar
    terryg752 Posts: 197, Reputation: 4
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    #2

    Nov 20, 2007, 05:39 PM
    (Conservation of energy is unlikely to help as in such cases as much enegey is lost in generating heat etc.)

    Use formula v^2 - u^2 = 2 fs

    0 - 22^2 = 2 f 1.20

    acceleration = f = - 22^2/2.40

    Force = mass times acceleration
    tjsail's Avatar
    tjsail Posts: 12, Reputation: 4
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    #3

    Nov 27, 2007, 03:00 PM
    And for part (a) you can use
    x = (Vo + Vf)*t/2
    where x is distance, Vo is original velocity, Vf is final velocity, and t is time - your unknown. Note: (Vo + Vf)/2 is average velocity, so when you multiply that by the time to stop, that's the distance traveled.
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