Question

A stone is dropped from a cliff into a lake 80 m deep another cliff 20 m away from the lake reflects the sound of the splash . what is the time difference between the two? take the speed of sound as 340 ms1 and g=10 ms 2

Answer 1

Answer:

Let S is depth of well and the dropped stone takes t1 seconds to reach the water surface. The we have

 S = (1/2)×9.8×t12 = 4.9×t12  ....................(1)

 let t2 be the time taken for the sound to reach observer. then we have

 t2 = S/352.8  ..................(2)

 substiute for S in (2) using (1)

 t2 = (4.9×t12)/352.8 = t12/72 ........(3)

 we are given t1+t2 = 25/8...........(4)

 using (3) in (4),  t1 + t12 / 72 = 25/8 ...(5)

by solving this quadratic equation (5) , we get t1 = 3 second.

 Hence the depth S can be obtained from (1) : S = 4.9×3×3 = 44.1 m

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Answer 2

Answer:

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