A rotating disk siren with 16 equally spaced holes produces sound at 320 Hz. A 24-hole disk rotates at 4/3 of the former rate. If the sound frequency is 320n Hz, find n.
Physics · Mixed Chapter
JEE Main Practice

Question

A rotating disk siren with 16 equally spaced holes produces sound at 320 Hz. A 24-hole disk rotates at 4/3 of the former rate. If the sound frequency is 320n Hz, find n.

G1 Physics · Accepted Answer

Step 1 — Siren frequency = (holes per revolution) × (revolutions per second). Step 2 — First disk rotates at 320/16 = 20 rev s⁻¹. Step 3 — Second disk speed is (4/3) × 20 = 80/3 rev s⁻¹. Step 4 — f₂ = 24 × (80/3) = 640 Hz = 320 × 2 Hz, so n = 2.