A train can deccerate at 0.4 m/s. It's traveling at 160km/hr. How far in advance should it apply brakes to come to a full stop.

Answer 1

v = Vi + a t
v = 0 at stop and Vi = 160,000/3600 = 44.4 m/s
so

0 = 44.4 - .4 t
t = 111 seconds

how far in 111 seconds
You can use d = Vi t + (1/2) a t^2
but it is easier just to use the average speed during the stop.
Vav = (44.4 + 0)/3 = 22.2 m/s
d = 22.2 * 111 = 2467 meters
or
2.467 km

Answer 2

This is terrible... this is all wrong! 1) it is (44.4+0)/2 not 3.
I unno how hell you got 111.. but 44.4 + (-.4m/s)^2 is not 111...
and 22.2 x 111 is not 2467... it is 2464.2

Answer 3

lol