Question

The freqeancy of sound produced by the horn of vertical 680Hz when the vertical approached the stationary observer the frequency of speed heard by the observer is 700Hz find the speed of the vehicle

Answer 1

Given :

Original frequency of sound wave = 680Hz

Apparent frequency of sound wave = 700Hz

Source of sound is moving towards stationary observer.

To Find :

Speed of the vehicle (source of sound).

Solution :

❒ Apparent frequency of a sound heard by listener when source of sound is moving towards stationary listener is given by

• f' = [v / (v - v｡)] × f

where,

• f' denotes apparent frequency

• f denotes original frequency

• v denotes speed of sound

• v｡ denotes speed of source

• We know that speed of sound in still air is 340 metre per second$.$

Remember : All the velocities are taken positive in the source to observer (s → o) direction and negative in the opposite (o → s) direction.

★ By plugging the given values,

⇒ 700 = [340 / (340 - v｡)] × 680

⇒ 340 / (340 - v｡) = 700/680

⇒ 340 - v｡ = 340 × 680/700

⇒ 340 - v｡ = 330.28

⇒ v｡ = 340 - 330.28

⇒ v｡ = 9.72 m/s