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#planetary orbit

2 public questions tagged with this topic.

What distinguishes the oscillatory nature of a pendulum from the periodic motion of a planet in orbit?

**Damped oscillations** occur when resistive forces dissipate energy, amplitude decays exponentially as A(t) = A₀ e^(-b t/2m), b damping coefficient (kg/s), frequency slightly reduced ω' = √(ω₀² - (b/2m)²). Damping arises from friction or viscosity, energy loss per cycle proportional to velocity squared, motion eventually stops. A pendulum oscillates about a fixed point due to a linear restoring force (gravity component), while a planet’s orbit is periodic but governed by inverse-square gravitational force. Applying x = A cos(ωt + φ), v = -ωA sin(ωt + φ), a = -ω²x and E = ½kA² = ½mω²A², result The restoring force is linear follows, reflecting SHM dependence

Ref: NCERT > Physics Book > Oscillations > Damped Oscillations

A planet orbits the Sun with a period of 5 years. If Earth’s orbital radius is 1.5×1011m, what is its semi-major axis?

Kepler’s third law: Tp2TE2 = ap3aE3. TE = 1year, Tp = 5years, aE = 1.5×1011m. 5212 = ap3(1.5×1011)3. 25 = ap33.375×1033. ap3 = 25×3.375×1033 = 8.4375×1034. ap = (8.4375×1034)1/3≈4.39×1011m. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 4.4 × 10¹¹ m. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: Halliday & Resnick, Fundamentals of Physics, 11th ed., Chapter 13: Gravitation.