Physics
posted by Anonymous .
solve physics question. a train moves 3.6km from rest to rest in 3minutes. the greatest speed is 90km/h, and the acceleration and retardation are uniform. find the distance travelled at full speed.

It sounds like the acceleration and deceleration are equal in value. So, since
90km/hr = 25m/s
3 min = 180 sec
3.6km = 3600m
If acceleration/deceleration take t seconds, leaving u seconds for fullspeed travel,
2t+u = 180
at = 25
at^2 + 25u = 3600
a = 25/3
t = 36
u = 108
so, going 25m/s for 108s = 2700m = 2.7 km