physics

A car of mass 100kg travelling with a velocity of 20mls was suddenly brought to rest 20m after application of break, find the average ating force and power expended by the engine.?

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  1. average speed during stop = 20/2 = 10 m/s
    went 20 meters so it took 2 seconds
    change in momentum/time = force
    100 * 20 / 2 = 1,000 Newtons
    power = change in energy/time = (1/2)(100) (20^2) /20= 10,000 watts
    or power = force * distance /time = 1000*20 /2 = 10,000 watts

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    Damon
  2. Thanks so much damon.

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  3. Given: M = 100 kg, Vo = 20 m/s.

    V^2 = Vo^2 + 2a*d = 0.
    20^2 + 2a*20 = 0,
    400 + 40a = 0,
    a = -10 m/s^2.

    F = M*a = 100 * (-10) = -1,000 N. The negative sign means the force opposed the action.

    V = Vo + a*t = 0.
    20 + (-10)t = 0,
    t = 2 s.

    P = F*d/t = 1000 * 20/2 = 10,000 Joules/s = 10,000 Watts.

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