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Question

A train travels from a city A to city B with a constant speed of 10 m/s and returns back to city A in half of the time taken to travel from A to B. Find its average speed during the entire journey.

A
40 m/s
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B
30 m/s
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C
15 m/s
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D
403 m/s
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Solution

The correct option is D 403 m/s
Let distance between the two cities A and B be x m.
Speed of train while going from A to B=10 m/s
Time taken by train to travel from A to B
t1=x10
and time taken by train to travel from B to A
t2=t12=x20

Average speed =total distancetotal time
vavg=x+xx10+x20
vavg=2xx10+x20=403 m/s

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