Question

A whistle producing sound waves of frequencies 9500 Hz and above is approaching a stationary person with speed v ms^-1. The velocity of sound in air is 300 ms^-1. If the person can hear frequencies up to a maximum of 10,000 HZ, the maximum value of v up to which he can hear the whistle is ______.

Options

• `15sqrt2` ms^-1

• `15/sqrt2` ms^-1

• 15 ms^-1

• 30 ms^-1

Answer 1

A whistle producing sound waves of frequencies 9500 Hz and above is approaching a stationary person with speed v ms^-1. The velocity of sound in air is 300 ms^-1. If the person can hear frequencies up to a maximum of 10,000 HZ, the maximum value of v up to which he can hear the whistle is 15 ms^-1.

Explanation:

Apparent frequency v' = v`["v"/("v" - "v"_"s")]`

⇒ 10000 = 9500`[300/(300 - "v")]` ⇒ 300 - v = 300 × 0.95

⇒ v = 300 - 285 = 15 ms^-1