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A train is speeding along a straight, level track at +20.0 m/s when the engineer applies the brakes, which results in an acceleration of -0.894 m/s2 as long as the train is in motion. How far does the train move during the 70 sec after the brakes are first applied?

  • physics - ,

    Key phrase is “as long as the train is in motion”: it moves during the time interval t<70 s.
    The train stops after t seconds of braking
    t=(v-vₒ)/a=( 0-20)/(-0.894)=22.4 s.
    s= vₒt-at²/2 =20•22.4 – 0.894•22.4²/2=223.7 m

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