An engineer in a locomotive sees a car stuck on the track at a railroad crossing in front of
the train. When the engineer first sees the
car, the locomotive is 330 m from the crossing
and its speed is 21 m/s.
If the engineer’s reaction time is 0.44 s,
what should be the magnitude of the minimum deceleration to avoid an accident?
Answer in units of m/s
2
.

Ai think hope that

Distance covered = speed x timethe distance traveled going against the stream = distance traveled with the stream.therefore it is the speed and the time that are the variables.as he travels the same distance both ways, speed x time is the same for each way.going upstream his speed is 4 kph; going downstream his speed is 6 kph.therefore we have two simultaneous equations: time upstream x 4 = time downstream x 6time upstream + time downstream = 60 minutestherefore we have the equation: time upstream = 6/10 hour, time downstream therefore = 4/10 hour.distance traveled at 4km/hr in 6/10 hour = 24/10 = 2.4km.check: distance traveled at 6km/hr in 4/10 hour = 24/10 = 2.4km.