Question

answer of ques 9 pls.
.worth 100 points

Answer 1

hey....

dude.......

8...The engine of the train is the first point that is entering the bridge, then, the whole train passes and finally the last point in the train crosses the bridge. 

So, total distance covered by the train = Length of bridge + it's own length = (200+400)m = 600 m... .....
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9.... similar to that question
.....

since equal distances are covered at 60 kmph and 40 kmph, we can apply the formula 2xy/(x+y)
Average speed= 2×40×6040+602×40×6040+60 = 48 kmph

This formula works as follows

Let the distance to one side = x
Total distance = 2x 

Time taken for the forward journey = x60x60
Time taken for the return journey = x40x40
Total time = x60+x40=100x2400x60+x40=100x2400

Average speed = Total distanceTotal Time=2x(100x2400)Total distanceTotal Time=2x(100x2400) = 48 kmph.
Speed = 36 kmph = 10m/s 
Hence, time taken = 600/10 s = 60s = 1min......

hope it helps....

Answer 2

hope it helps you
please mark it as brainliest