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    PnoyDeadpool's Avatar
    PnoyDeadpool Posts: 1, Reputation: 1
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    #1

    Oct 13, 2011, 12:21 PM
    Friction... please help
    A pick up truck is travelling at 58 km/h on a dry horizontal concrete surface when the driver applies the brakes locking the wheels. (a) How far does the car travel before coming to rest? (b) How long does it take the car to stop after the driver applies the brakes? (c) How far does the car travel before coming to rest if the concrete surface is wet?

    Coefficient of friction
    Rubber on dry concrete:
    Static: 0.948 kinetic: 0.709

    Rubber on wet concrete:
    Static: 0.718 kinetic: 0.522
    Unknown008's Avatar
    Unknown008 Posts: 8,076, Reputation: 723
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    #2

    Oct 13, 2011, 11:53 PM
    Use the coefficient of kinetic friction when you have a moving body coming to rest.

    So, find the deceleration of the truck using F = ma

    Then use the kinematic equation of motion to get the stopping distance.


    Alternatively, use the energy equations, where the work done against friction minus the initial kinetic energy of the truck should give 0.

    Either way should give you the same answer :)

    Can you post what you get?

    Also Frictional force = Coefficient x Normal reaction on the truck
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