A constant force acting on a body of mass 5 kg changes its speed from 2 m/s to 8 m/s in 10 s. The magnitude of force is MCQ with Answer and Explanation

Explanation:
Work done by a variable force is the definite integral of F dx. W = Integral(3x^2 + 2x) dx from 1 to 2. W = [x^3 + x^2] evaluated from 1 to 2. Upper limit: (2^3 + 2^2) = 8 + 4 = 12. Lower limit: (1^3 + 1^2) = 1 + 1 = 2. Work = 12 - 2 = 10 Joules.

Explanation:
For spring-mass system undergoing SHM, time period T = 2π√(M/k), derived from F = -kx = Ma ⇒ a = -(k/M)x, so ω² = k/M, T=2π/ω=2π√(M/k). Option B has inverse ratio; C misses factor 2; D is for pendulum. Memory tip: 'Spring: T ∝ √(M/k); Pendulum: T ∝ √(l/g)'. This standard formula is frequently tested in oscillations sections of competitive exams. Always verify dimensions: √(kg / (N/m)) = √(kg·m/N) = √(s²) = s, correct for time period.

Explanation:
LED (Light Emitting Diode) works on electroluminescence: when electrons recombine with holes in a semiconductor junction, energy is released as photons. This is distinct from incandescence (heating filament, like bulbs), fluorescence (absorb UV, emit visible), or heating effect. Memory aid: 'LED = semiconductor light emission; no filament'. This modern application question tests knowledge of everyday physics, common in competitive exams. Always link device to underlying phenomenon: LED (electroluminescence), laser (stimulated emission), solar cell (photovoltaic effect).