Satellite orbital velocity v = √(GM/r). If radius doubles, velocity becomes: MCQ with Answer and Explanation

Explanation:
Ferromagnetic materials have μ_r >> 1 (hundreds to thousands). Paramagnetic slightly >1, diamagnetic

Explanation:
SONAR (Sound Navigation and Ranging) uses ultrasonic waves (frequency > 20 kHz) because they have high directionality, short wavelength for better resolution, and minimal absorption in water. Radio waves attenuate rapidly in water; infrasonic waves have long wavelengths unsuitable for detection; light doesn't propagate far in water. Memory tip: 'Ultra = beyond human hearing; used in SONAR/ultrasound imaging'. This application question tests knowledge of wave frequency ranges and their practical uses, common in competitive exams linking physics to technology. Always recall frequency thresholds: infrasonic 20kHz.

Explanation:
Acceleration due to gravity at height h: g' = gR²/(R+h)², where R is Earth's radius. Given h = R, so g' = gR²/(2R)² = gR²/4R² = g/4. This inverse square law dependence arises from Newton's law of gravitation. At depth, variation differs, but for height, this formula applies. Memory aid: Double the distance from center ⇒ gravity becomes one-fourth. This standard result is frequently tested in gravitation sections of competitive exams. Always verify whether height or depth is specified, as formulas differ significantly.