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Elastic potential energy E = (1/2)kx². 5 = (1/2)k(0.1)². 5 = 0.005k. k = 1000 N/m.

Using v = fλ, where v = 330 m/s and f = 440 Hz. λ = v/f = 330/440 = 0.75 m.

For parallel resistances: 1/R = 1/R₁ + 1/R₂ = 1/10 + 1/20 = 3/20. Therefore R = 20/3 = 6.67 Ω.

When object distance (5 cm) < focal length (10 cm), the object is between the mirror and focus. A concave mirror forms a virtual, erect, and magnified image in this case.

Gravitational force is always attractive, acts between any two masses, is independent of the medium, and is governed by Newton's law of universal gravitation.

Using v = u + at, where u = 0, v = 20 m/s, a = 2 m/s². 20 = 0 + 2t, so t = 10 seconds.

At sunset, light travels through a longer path in the atmosphere. Shorter wavelengths (blue) scatter more (Rayleigh scattering), leaving longer wavelengths (red) to reach the observer.

Using lens formula: 1/f = 1/u + 1/v. 1/15 = 1/30 + 1/v gives v = 30 cm. When u = 2f, image forms at 2f with magnification -1 (same size, inverted, real).

Electric potential is defined as work done per unit charge. SI unit is Joule/Coulomb = Volt. Option D (Watt/Ampere) also equals Volt but option A is more fundamental.

Acoustic impedance (Z) = ρ × c, where ρ is density and c is sound velocity. SI unit is kg/(m²·s). It's crucial for understanding sound reflection and transmission.