Hello,
First of all convert the speed of the train in m/s
So 45 kmph = 12.5 m/s
Now the distance the train would cover in 30 seconds can be found out by using the simple maths ie distance = speed × Time.
so distance covered by train = 12.5× 30 = 375m.
Now the train will cross the bridge completely when It accomplishes the following journey-
"The engine was at the beginning of the bridge and after crossing the bridge the last coach was at the other end of bridge".
Hence we will subtract length of train from total distance.
So the length of the bridge = 375-130 = 245m
Hi
Answer :- the bridge's length is 245 m
EXPLANATION
We have
Speed= 45 km/ hr
= (45× 18/ 5 )m/sec
= 25/2 m/sec
Now, time = 30 sec.
Let us assume the length of bridge be x.
Then,
Distance/ time = speed
130+x/ 30 = 25/2
Or 2(130+x)=750
Or x=245m
Hence, length of the bridge is 245 m
Thank you
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