Question

The minimum distance of reflected surface from the source for listening the echo of sound is
(a) 28 m
(b) 18 m
(c) 19 m
(d) 16.5 m

Answer 1

d) 16.5m
Minimum distance required will be 16.5 m. To verify this, use the formula speed is equals to distance upon time. Our ears can differentiate between two sounds if there is difference of at least one-tenth of a second between two sounds. Put this as time and put speed of sound in air in above formula to get answer.

Answer 2

D is the correct answer.