Question:

The longest and the shortest distance of our planet from sun is and $R_1$ and $R_2$. Distance from sun when it is normal to major axis of orbit is .

Updated On: Jun 7, 2022
  • $\frac{R_1+R_2}{2}$
  • $\sqrt{\frac{R^2_1+R^2_2}{2}}$
  • $\frac{R_1R_2}{R_1+R_2}$
  • $\frac{2R_1R_2}{R_1+R_2}$
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The Correct Option is D

Solution and Explanation

$r_1 = (1 +e) a ;r_2 = (1 - e) a$
$ a = \frac{r_1+r_2}{2} ; r_1r_2 = (1 - e^2)a^2$
= $\frac{b^2}{a}$
$= \frac{a^2(1 - e^2)}{a} = \frac{r_1r_2}{\frac{r_1+r_2}{2}} = \frac{2r_1r_2}{r_1+r_2}$
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Concepts Used:

Keplers Laws

Kepler’s laws of planetary motion are three laws describing the motion of planets around the sun.

Kepler First law – The Law of Orbits

All the planets revolve around the sun in elliptical orbits having the sun at one of the foci.

Kepler’s Second Law – The Law of Equal Areas

It states that the radius vector drawn from the sun to the planet sweeps out equal areas in equal intervals of time.

Kepler’s Third Law – The Law of Periods

It states that the square of the time period of revolution of a planet is directly proportional to the cube of its semi-major axis.

T2 ∝ a3