Q 11-07-032NEETJEE MainMedium
A planet moves in an elliptical orbit around the Sun. Its distances from the Sun at perihelion and aphelion are $r_1$ and $r_2$. The ratio of its speeds at perihelion and aphelion is
Answer: (D) $\dfrac{r_2}{r_1}$
Concept. Angular momentum is conserved; at perihelion and aphelion $\vec v \perp \vec r$.
Step 1. Equation. $mv_1r_1 = mv_2r_2$.
Step 2. Ratio. $\dfrac{v_1}{v_2} = \dfrac{r_2}{r_1}$.
Answer. $\dfrac{r_2}{r_1}$ (Option D).
Solution by Sreeraj P, M.Sc Physics