Two rifles are fired from the same place at a difference of 11 minutes 45 seconds. But a man who is coming towards the place in a train hears the second sound after 11 minutes. Find the speed of train. (speed of sound = 330 m/s)

A) 72 kmph B) 36 kmph C) 81 kmph D) 108 kmph E) None of these

Answer & Solution

Correct Answer: Option C

Distance travelled by man-train in 11 minute = distance traveled by sound in (11 min 45 sec - 11 min) = 45 sec.
Let the speed of train be x kmph.
Now,
Or, $$x \times \frac{{11}}{{60}} = \frac{{45}}{{3600}} \times 330 \times \frac{{18}}{5}$$
Or, x = 81 kmph.

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3 Comments

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Sheero Doley 10 years ago

Need more explanation

Kumar Chandan 11 years ago

Actually, here is concept of relative speed of Man-Train and Sound. It also includes relative time. See, both are approaching to each other it means the must be subtracted. To find the relative time as we do in relative speed.

Tanzid Ahmed 11 years ago

Please explain how it happens " distance travelled by man train in 11 minute=distance traveled by sound in (11min45-11min)"

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Two rifles are fired from the same place at a difference...

Two rifles are fired from the same place at a difference of 11 minutes 45 seconds. But a man who is coming towards the place in a train hears the second sound after 11 minutes. Find the speed of train. (speed of sound = 330 m/s)

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