A siren placed at a railway platform is emitting sound of frequency 5 ...
Given:
Frequency of siren at the railway platform, f = 5 kHz
Frequency heard by passenger in train A while approaching the siren, f₁ = 5.5 kHz
Frequency heard by passenger in train B while approaching the siren, f₂ = 6.0 kHz
We need to find the ratio of the velocity of train B to that of train A.
Let's assume:
v₁ = velocity of train A
v₂ = velocity of train B
v = velocity of sound in air
We know that the apparent frequency heard by an observer moving towards a source of sound is given by:
f₁ = (v + v₁) / (v - v)
Similarly, the apparent frequency heard by an observer moving towards a source of sound is given by:
f₂ = (v + v₂) / (v - v)
We can rearrange the above equations to solve for v₁ and v₂:
(v + v₁) = f₁(v - v)
(v + v₂) = f₂(v - v)
Dividing the above equations, we get:
(v + v₁) / (v + v₂) = f₁ / f₂
Substituting the given values, we have:
(5v + 5v₁) / (5v + 5v₂) = 5.5 / 6.0
Simplifying the equation, we get:
(1 + v₁/v) / (1 + v₂/v) = 11/12
Cross-multiplying, we have:
12 + 12(v₁/v) = 11 + 11(v₂/v)
Rearranging the equation, we get:
v₁/v - v₂/v = -1/12
Dividing throughout by v, we have:
v₁ - v₂ = -v/12
Dividing throughout by v₁, we get:
(v₁ - v₂)/v₁ = -v/12v₁
Simplifying the equation, we have:
1 - v₂/v₁ = -1/12
Rearranging the equation, we get:
v₂/v₁ = 1 - 1/12
Simplifying the equation, we have:
v₂/v₁ = 11/12
Therefore, the ratio of the velocity of train B to that of train A is 11/12, which is approximately 0.917.
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