Question

Two boys are separated by a distance 50 m and are standing away from a vertical wall. When one of the boys claps, the other boy hears the echo after 1s. If velocity of sound in air is 330 ms^–1 then distance of the boy from the wall is -

• A. 330 m
• B. 818 m
• C. 188 m
• D. 881 m

Answer 1

Answer: (C)

188 m

Answer 2

time for direct sound

t₁ = $\frac{AB}{330}$ = $\frac{50}{330}$ ……. (1)

time to travel APB

t₂ = $\frac{2AP}{330}$ ; Dt = 1 = $\frac{2AP}{330}$ – $\frac{50}{330}$

\ AP = 190 m

PQ = $\sqrt{190^{2}–25^{2}}$= 188 m