physics
posted by akanksha .
a train 100m long is to cross a river bridge of length 800m. what time it take to cross the bridge ?velocity of train is 36km/h.

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 
(a)800 m. (b)1000 m.(c)1500 m.(d)2600 m.