Physics-
General
Easy

Question

A man standing between two parallel hills, claps his hand and hears successive echoes at regular intervals of 11s If velocity of sound is 340 m s to the power of negative 1 end exponent comma then the distance between the hills is

  1. 100m    
  2. 170m    
  3. 510m    
  4. 340m    

The correct answer is: 510m


    Let the man M be at a distance x from hill H subscript 1 end subscript and y from hill H subscript 2 end subscript as shown in figure. Let y greater than x.

    The time interval between the original sound and echoes from H subscript 1 end subscript and H subscript 2 end subscript will be respectively
    t subscript 1 end subscript equals fraction numerator 2 x over denominator v end fraction and t subscript 2 end subscript equals fraction numerator 2 y over denominator v end fraction
    where v is the velocity of sound
    The distance between the hills is
    x plus y equals fraction numerator v over denominator 2 end fraction open parentheses t subscript 1 end subscript plus t subscript 2 end subscript close parentheses equals fraction numerator 340 over denominator 2 end fraction open square brackets 1 plus 2 close square brackets equals 510 blank m

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