Question

Q.14) A boy is standing in the middle between the two vertical cliffs and shouting. The total distance
between the cliffs is 800m. The boy hears the first echo after 4 seconds and the second echo 3 seconds later.
Calculate the speed of the sound for both the waves.​

Answer 1

Explanation:

Now, we know it takes the sound 0.8 sec. to do the distance. Right? The speed being 340 m/s, we can deduce the distance is (0.8*340 = 272 m). Still following?

But the sound leaves the boys hands, goes to the cliff where it's reflected and comes back to the boy's ears. This is the principle of the echo: soundwaves go forth and back, hence, one could make the mistake and forget this. The sound took 0.8 seconds to do 272m, but these were from the boy to the cliff AND BACK.

So, if the total distance, forth and back, is 272 m, the boy stands at (272/2 = 136m) from the cliff. Most important is not that you have collected the answer to your homework, but that you've understood and will be able to redo the calculation next time

Answer 2

Explanation:

Total distance by time coming and going back(in the case of nearest cliff)=2×480m

speed of sound =

Total Distance Travelled/Timer taken=2×480/3

=320m

time taken to reach second echo 3+2=5 sec

now v=2d/t

d=vt/2

diffrent of other cliff for the person

=320×5/2

=800m