Which of the following is a derived unit? MCQ with Answer and Explanation

Explanation:
Planck's constant h = E/ν. Dimensions: [ML²T⁻²]/[T⁻¹] = [ML²T⁻¹]. Angular momentum = mvr = [ML²T⁻¹]. Linear momentum [MLT⁻¹], force [MLT⁻²], energy [ML²T⁻²]. So angular momentum matches. This is a frequently asked SSC question.

Explanation:
Higher frequency → higher pitch. Amplitude increases loudness. Wavelength inversely proportional to frequency (v constant). So increasing frequency increases pitch.

Explanation:
This is the Doppler effect: when source moves toward observer, wavefronts compress, decreasing wavelength, thus increasing apparent frequency (f' = f·v/(v - v_s), where v is sound speed, v_s source speed). Conversely, receding source decreases frequency. This applies to all waves (light, sound). Memory aid: 'Approaching = higher pitch (frequency); Receding = lower pitch'. Competitive exams often test qualitative understanding before formula application. Always identify motion direction relative to observer for sign conventions in numerical problems.