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26 July, 07:45

An 800 kg car is moving at 32 m/s. What magnitude force is needed to bring that car to a stop in 30 seconds?

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  1. 26 July, 08:04
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    Kinematic relationship to get acceleration:

    vf2 - vi2 = 2ax

    vf = final speed = 0 m/s (comes to a full stop)

    vi = initial speed = 32.0 m/s

    x = distance over which the accelerating force acts to bring about a full stop = 30.0 m

    a = acceleration

    a = - vi2 / (2x) = - (32.0 m/s) 2 / [2 (30.0 m) ] = - 17.06 m/s2

    The negative sign indicates it is a deceleration.

    Newton's 2nd law:

    F = ma = (800 kg) (-17.06 m/s2) = - 13648 N

    The negative sign indicates the force is opposing the direction of motion. The magnitude of the force is

    |F| = 13648 N
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