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#1 2005-10-21 18:51:08



problem time & distance

the problem is .

Two  guns were fired from the same place at an interval of 17 minutes but a person in a train approaching the place hears the second report 16 minutes and 30 seconds after the first . supposing that the sound travels at the speed of 330 mts per second , find the speed of the train

#2 2005-10-21 21:01:57



Re: problem time & distance

Well, if you were standing still some distance away you would have the first sound reach you as the other was still travelling toward you at 330 m/s.

If you could speed up the other sound, for example by moving towards it, you could get to hear it sooner.

At 330 m/s, it would take 17 min.
At (say) 660 m/s it would take 8.5 mins (double the speed and halve the time)

So, I can figure that the relative speed should be 330 * (17/16.5) = 340 m/s

In other words, at 340 m/s, it would take 17 * 330/340 = 16.5 mins.

So, you would have to "speed up" the sound by simply moving towards it at 10 m/s

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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