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⚛️ Physics  ·  System of Particles and Rotational Motion  ·  NEET & JEE

Which conservation law explains why a planet moves faster when closer to the Sun?

Answer: Conservation of angular momentum.

  • A Conservation of angular momentum
  • B Conservation of linear momentum
  • C Conservation of energy
  • D Conservation of mass

Correct answer: A. Conservation of angular momentum

Explanation: As the planet gets closer to the Sun, r decreases, so v must increase to keep L = mvr constant (Kepler's second law).

axis OPr⊥Fττ = r⊥ × F = r × F × sinθ

Torque about axis O equals the force F multiplied by the perpendicular distance r⊥ from the axis to the line of action of the force, producing rotation.

Concept context

Moment of inertia, torque, angular momentum, rolling motion. Very high JEE weightage.

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