Q.

A satellite is orbiting just above the surface of the earth with period T. If d is the density of the earth and G is the universal constant of gravitation, the quantity 3πGd represents:                    [2023]

1 T3  
2 T  
3 T  
4 T2  

Ans.

(4)

Let the planet is moving above the earth surface at R distance.

T=2πRv                                 ...(i)

As, the centripetal force of satellite is due to gravitational force of earth.

GMmR2=mv2RGMR=v2  or  v=GMR

Using (i), T=2πRRGM

T2=4π2R3G(d×43πR3)=3πGd.  Hence,  3πGd=T2