If the beat frequency is n (beats per second), then in two seconds the number of beats is 2n.

Wind in the same direction adds to the effective propagation speed of sound, increasing its measured speed.

18 beats in 3 s → 6 beats/s, and beats decrease when siren frequency decreases implies fork frequency is lower than siren: f_t = 256 - 6 = 250 Hz.

A pipe closed at one end supports only odd harmonics (odd-numbered harmonics) for standing waves.

Sound in air consists of compressions and rarefactions along the direction of propagation, characteristic of longitudinal waves.

If T increases to 1.69T, L must increase by factor √1.69 = 1.3, i.e. a 30% increase to keep f (∝ √T / L) constant.

An echo requires a delayed return of >0.1 s; with sound speed ~343 m/s, the reflector must be roughly 17 m away, so 16.5 m is the closest option.

Source speed = 2 rev/s × 2π ×1 m = 4π ≈ 12.57 m/s; frequency ratio ≈ (c+v)/(c-v) ≈ (332+12.57)/(332-12.57) ≈1.078 ≈ 1.08:1.

Ultrasonic waves have frequencies above human hearing range and thus cannot be heard by humans unaided.

A tuning fork vibrates and produces mechanical oscillations in air, generating sound.