Question

A man is standing between source and cliff. When he start moving along line joining him and source, he hears 10 beats per second. Velocity of man is : (Frequency of source = 60 Hz, Velocity of sound = 330 m/s)

• A. 5 m/s
• B. 10 m/s
• C. 15 m/s
• D. 2.5 m/s

Answer 1

Answer: (D)

2.5 m/s

Answer 2

Frequency of echo as heard by man

n₁ = $\frac { \mathrm { v } + \mathrm { v } _ { 0 } } { \mathrm { v } }$ × n₀

[n₀ = Frequency of sound

v₀ = Velocity of man

v = Velocity of sound]

Frequency of sound heard by man directly from source

n₂ =.n₀

n₁ – n₂ = 10

\ v₀ = $\frac { v \times 10 } { 2 \times v _ { 0 } }$= 2.5 m/s