CSIR UGC NET June 2019 Central Force Problem

The problem goes like this:

The problem goes something like this:
Assume that the Earth revolves in a circular orbit around the sun suppose the gravitational constant G very slowly as a function of time in particular it decreases to half its initial value in the course of 1 million years then during this time :
a)Radius of the earth’s Orbit will increase by a factor of 2
b) Total energy of the earth remains constant
c) orbital angular momentum of the earth will increase
d) radius of the earth’s Orbit remains the same.

here a solution to this problem:

If you do not have Data pack to watch the video, you can even check out my slides here 👇

Csr ugc net phy june19 physics q(6 of 55) solution from Bibhatsu Bibhatsu

Check out and download the solution slide 👇