A train travels from a city A to city B with a constant speed of 10m/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
40m/s
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B
30m/s
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C
15m/s
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D
403m/s
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Solution
The correct option is D403m/s Let distance between the two cities A and B be xm. Speed of train while going from A to B=10m/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=403m/s