A car that weighs 15,000 N is initially moving at 60 km/hr when the brakes are applied. The car is brought to a stop in 30 m. Assuming the force applied by the brakes is constant, determine the magnitude of the braking force.

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  1. Force x (stopping distance)
    = (initial kinetic energy)
    = (1/2) M V^2

    For the kinetic energy, you will have to convert the weight (N) to mass (kg) and the 60 km/hr initial velocity to m/s. I assume you know how to do this.

    Your answer, MV^2/(2X) will be in Newtons.

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  2. Thanks you for your quick reply. I really appreciated it, although I still cannot find the way to get the answer which is 7,086.7 N.

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  3. m = 15,000/9.8 = 1530 kg
    v = 60,000 m/3600 s = 16.7 m/s

    (1/2) m v^2 = 212,500 Joules

    F (30) = 212,500
    F = 7083 N

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  4. Make certain you convert the weight 15000N to mass.

    Force= .5 M V^2/distance=
    = .5 (Weight/g)V^2 /distance3=
    = .5(15,000/9.8)*16.66^2 /30
    and that gives the right answer.

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