Practice question

**Relative motion** changes effective wavelength encountered. For moving source approaching stationary observer, wavelength ahead λ' = (v - v_s)/f, so f' = v/λ' = f·v/(v - v_s) > f, basis for calculating apparent pitch shift in sound. Linear mass density: μ = (0.06/3) = 0.02 kg/m . Speed: v = √((T/μ)) = √((150/0.02)) = √(7500) ≈ 86.6 m/s . Using v = fλ and standing-wave condition fₙ = n v/(2L) or v/(4L) as applicable, calculation yields 86.6 m/s, illustrating frequency-length-speed interdependence and quantization by boundaries.