Question

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?

Answer 1

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