MHT CET 2021 Physics Solved Paper

(a) According to deduction of Kepler's third law and with the help of Newton's law, the law of period is given by
‌ or ‌‌T2=‌

4π2

GM

r3
⇒T=2π√‌

r3

GM

where, r is the radius of orbit and M is mass of the planet or star.
As satellite is very close of the planet, thus r=R
Also mass (M)= density (ρ)× volume (V)
‌‌=ρ×‌

4

3

πR3
∴‌‌T‌‌=2π√‌

R3

G×‌ 4 3 πR3

=√‌

3π

ρG