A man standing in front of mountain at a certain distance beats a drum at regular intervals. The drumming rate is gradually increased and finds that the echo is not heard distinctly when the rate becomes 40 per minute. If the velocity of sound in air is 340 m/s, then the distance between the man and mountain is

Options

A. 133.3 m
B. 255 m
C. 510 m
D. none of these

Answer

B

Explanation

`n = (40)/(60) = (2)/(3) :. T = (1)/(n) = (3)/(2)`
`2x = vT = 340 xx (3)/(2)`
`2x = 510 m`
`x = (510)/(2) = 255 m`