Question

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Q7. A train 100 m long is to cross a river bridge of length 800 m. What time will it take to cross a bridge?
Given that the train moves with a constant velocity of 30 km/h​

Answer 1

length of train=100m

length of bridge=800m

total distance=length of train+length of bridge

100+800=900m

velocity=30kmph=25/3m/s

Now

velocity=distance/time=900/25/3

now time=distance/velocity

=(900*3)/25

=2700/25

=108sec

or 1minute48seconds

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 = 30 km/h = 30 × 5 / 18 = (25 / 3) m/s

Hence the time taken to cross the bridge is,

t = 900 / (25/3) = 108 s.