A whistle sends out 256 waves in a second. If the whistle approaches the observer with velocity (1/3)rd of the velocity of sound in air. The number of waves per second observer will receive is (a) 384 (b) 192 (c) 300 (d) 200

Answer: (a). Source approaching: n' = n(v)/(v - vs). n' = 256 × (v)/(v - v/3) = 256 × 3/2 n' = 384 waves per second. So the answer is (a) 384.

A whistle sends out 256 waves in a second. If the whistle approaches… | MHT CET 2026 (13 May, Shift 1)

Q1MHT CET 2026 · 13 MAY · SHIFT 1Easy

Doppler Effect

A whistle sends out 256 waves in a second. If the whistle approaches the observer with velocity $\left(\frac{1}{3}\right)^{rd}$ of the velocity of sound in air. The number of waves per second observer will receive is

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Answer: (a)

Source approaching: $n' = n\frac{v}{v - v_s}$ .
$n' = 256 \times \frac{v}{v - v/3} = 256 \times \frac{3}{2}$
$n' = 384$ waves per second. So the answer is (a) $384$ .

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