A whistle of frequency 1000 Hz is sounded on a car travelling towards a cliff with velocity of 18 ms -1 normal to the cliff. If c=330 ms -1, then the apparent frequency of the echo as heard by the car driver is nearly

Question

A whistle of frequency 1000 Hz is sounded on a car travelling towards a cliff with velocity of 18 ms -1 normal to the cliff. If c=330 ms -1, then the apparent frequency of the echo as heard by the car driver is nearly (A) 1115 Hz (B) 115 Hz (C) 67 Hz (D) 47.2 Hz

Tardigrade Admin · Accepted Answer

By the concept of accoustic, the observer and source are moving towards each other, each with a velocity of 18 ms -1 ∴ v'=(330+18/330-18) × 1000 ≈ 1115 Hz

Q. A whistle of frequency $1000 Hz$ is sounded on a car travelling towards a cliff with velocity of $18 m s^{- 1}$ normal to the cliff. If $c = 330 m s^{- 1}$ , then the apparent frequency of the echo as heard by the car driver is nearly

$1115 Hz$

$115 Hz$

$67 Hz$

$47.2 Hz$

By the concept of accoustic, the observer and source are moving towards each other, each with a velocity of $18 m s^{- 1}$
$∴ v^{'} = \frac{330 + 18}{330 - 18} \times 1000 \approx 1115 Hz$

Q. A whistle of frequency 1000Hz is sounded on a car travelling towards a cliff with velocity of 18ms−1 normal to the cliff. If c=330ms−1, then the apparent frequency of the echo as heard by the car driver is nearly

1115Hz

115Hz

67Hz

47.2Hz