Question

A train 100m long is to cross a river bridge of length 800 metre?What time will it take to cross the bridge ?Given that the train moves with a constant velocity of 36 km/h?

Answer 1

Convert speed to m/s:

36 km/h = 36/3.6=10 m/s

In calculating train crossing bridges, we have to remember that after the head of the train has crossed the bridge (800 m), the remainder of the train is still on the bridge. So to completely cross the bridge, the time is what is takes to travel 800+100 metres.

Time required  

= (800+100)m /10 m/s

= 90 s

Answer 2

Total distance required for the train to cross the bridge is,

d = (100 + 800) m = 900 m

The speed of the train is,

v = 36 km/h = (36 × 5 / 18) = 10 m/s

Hence the time taken to cross the bridge is,

t = 900 / 10 = 90 s.