The change in momentum of a body is equal to MCQ with Answer and Explanation

Explanation:
Weight W = mg. On Earth: 10×10 = 100 N. On Moon: g_moon ≈ 10/6 ≈ 1.67 m/s². W_moon = 10×1.67 ≈ 16.7 N. Mass remains 10 kg; weight changes with gravity. Memory tip: 'Mass constant; weight ∝ g'. Tests mass-weight distinction and gravity variation, common conceptual question in competitive exams.

Explanation:
Radiation does not require medium; it travels via electromagnetic waves. Conduction needs medium for molecular collisions, convection needs fluid motion. Sun's heat reaches Earth by radiation through vacuum of space.

Explanation:
For spherical mirrors (concave or convex), focal length f = R/2, where R is radius of curvature. This holds under paraxial approximation (small angles). Derivation uses geometry of reflection and small-angle approximations. Memory tip: 'Mirror: f = R/2; Lens: 1/f = (n-1)(1/R₁ - 1/R₂)'. This fundamental relation is frequently tested in optics sections of competitive exams. Always note sign conventions: f negative for convex mirrors, positive for concave; R follows same sign as f.