Physics

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A 600kg car is moving on a level road at 30m/s.how large is a retarding force is required to stop it in a distance of 70m

  • Physics -

    speed:

    v = 30 + a t
    what is a when v = 0
    -30 = a t
    a = -30/t

    distance:
    70 = 30 t + (1/2) a t^2
    70 = 30 t -(15/t) t^2
    70 = 15 t
    t = 14/3 seconds to stop
    a = -30/t = -90/14 m/s^2 = -45/7

    then F = m a
    F = -600 (45/7) Newtons

  • Physics -

    There is a quicker way:

    vf^2=vi^2+2ad but a= forcefriction/mass

    0=30^2+2*force/mass * 70
    solve for force.

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