Q. A planet moving along an elliptical orbit is closest to the sun at a distance r₁ and farthest away at a distance of r₂. If v₁ and v₂ are the linear velocities at these points respectively, then the ratio v₁/v₂ is

A) r₁/r₂
B) (r₁/r₂)²
C) r₂/r₁
D) (r₂/r₁)²
Explanation

[Solution from source] Gravity exerts no torque about the sun, so angular momentum is conserved; at perihelion and aphelion the velocity is perpendicular to the radius, so mv₁r₁ = mv₂r₂ and v₁/v₂ = r₂/r₁. The planet moves faster when closer, so the ratio must exceed 1, which rules out r₁/r₂. Answer (3).

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.

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