For source moving toward observer at 0.1c, f' = f/(1 - 0.1) = f/0.9 ≈ 1.111×200 ≈ 222 Hz.

For open pipes f = v/(2L); beat frequency Δf = v(1/0.20 - 1/0.201)/2 = 5 ⇒ v ≈ 402 m/s.

The reflected frequency heard by the runner is f'(v+vs)/(v-vs); beat frequency = |f'−f| = 2f·vs/(v−vs). With f=272 Hz, vs=18 km/h=5 m/s and v=345 m/s this gives 8 beats/s.

Doppler radar measures velocity via frequency shift and is commonly used for speed monitoring of moving vehicles.

Critical angle satisfies sin θc = v1/v2 = v/(2v) = 1/2, so θc = 30°, the angle for onset of total internal reflection.

Doppler's effect is used in radar, sonar, and astronomy to measure relative speeds, so all listed applications apply.

Two equal-amplitude waves perfectly out of phase destructively interfere to give zero amplitude; the OCR shows option A marked.

Speed of sound in a gas depends on temperature and not on pressure alone for the same temperature, so the ratio is 1:1.

Temperature changes the speed of waves in the medium; for a source of fixed frequency (tuning fork) the wavelength changes accordingly.

Stress = E×strain gives T/A = (2×10^11)(0.01); wave speed v = √(T/μ) = √((E×strain)/ρ) ≈ 510 m/s, and f = v/(2L) ≈ 510/(3)=170 Hz.