Homework Help: Physics

Posted by Jennifer on Wednesday, September 15, 2010 at 8:08am.

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 210 m from the crossing
and its speed is 26 m/s.
If the engineer’s reaction time is 0.62 s,
what should be the magnitude of the mini-
mum deceleration to avoid an accident?
Answer in units of m/s2.

Physics - drwls, Wednesday, September 15, 2010 at 8:40am
During the engineer's reaction time, the train travels 26 x 0.62 = 16 meters. To avoid a collision after that, the train's speed must be reduced to zero while traveling less than 194 m.

While decelerating, the average speed will be 26/2 = 13 m/s

Maximum stopping time
= (194 m)/(13 m/s) = 14.92 s

Required deceleration rate
= (26 m/s)/14.92s = ____ m/s^2

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