# Physics

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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.

• Physics -

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 full-speed 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

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