13. A train travelling with uniform speedcrosses two bridges of length

1.	13. A train travelling with uniform speedcrosses two bridges of lengths 300 m and240 m in 21 sand 18 s, respectively. Findthe speed of the train. [SSC CPO 2011]
Answer» Let length of the train = L According to the question, L+30021=L+24018L+30021=L+24018 =>L+307=L+2406L+307=L+2406 => 6L + 1800 = 7L + 1680 Therefore, L = 120 m Taking the length of the 2nd bridge into consideration, Speed of train =L+24018=120+24018m/sL+24018=120+24018m/s =36018×185km/h36018×185km/h = 72 km/h

13. A train travelling with uniform speedcrosses two bridges of lengths 300 m and240 m in 21 sand 18 s, respectively. Findthe speed of the train. [SSC CPO 2011]

Answer»

Let length of the train = L

According to the question,

L+30021=L+24018L+30021=L+24018

=>L+307=L+2406L+307=L+2406

=> 6L + 1800 = 7L + 1680

Therefore, L = 120 m

Taking the length of the 2nd bridge into consideration,

Speed of train =L+24018=120+24018m/sL+24018=120+24018m/s

=36018×185km/h36018×185km/h

= 72 km/h