A man is lying on the floor of a large, empty hemispherical hall, in such a way that his head is at the centre of the hall. He shouts ''Hello'' and hears the echo of his voice after 0.2s. What is the radius of the hall ?

Explanation

Let the distance travalled by the sound wave = 2d m
Time to hear the echo `(t) = 0.2s` , Speed of sound (v) = 340 m/s
We know that `v = (2d)/(t)`
`implies 340 = (2 xx d)/(0.2) implies 2d = 340 xx 0.2`
`implies d = (340 xx0.2)/(2)` = 34 m.
As the head of the man is at the centre of hemispherical room, then 'd' is the radius of the hall.
Radius of the hall = 34 m.
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