Q. A planet moves around the sun. At a given point $P$, it is closest from the sun at a distance $d_{1}$ and has a speed $v_{1}$. At another point $Q$, when it is farthest from the sun at a distance $d_{2}$, its speed will be
A) $\frac{d_{1}^{2}v_{1}}{d_{2}^{2}}$
B) $\frac{d_{2}v_{1}}{d_{1}}$
C) $\frac{d_{1}v_{1}}{d_{2}}$
D) $\frac{d_{2}^{2}v_{1}}{d_{1}^{2}}$
Explanation
(c) Angular momentum remains constant
$mv_{1}d_{1} = mv_{2}d_{2} \Rightarrow v_{2} = \frac{v_{1}d_{1}}{d_{2}}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.