Q.

A satellite revolving around a planet in stationary orbit has time period 6 hours. The mass of planet is one-fourth the mass of earth. The radius orbit of planet is

(Given = Radius of geo-stationary orbit for earth is 4.2×104 km)          [2024]

1 1.05×104 km  
2 1.4×104 km  
3 1.68×105 km  
4 8.4×104 km  

Ans.

(1)   

        By Kepler's law, T2=4π2R3GMT2R3M

         (T1T2)2=(R1R2)3(M2M1)

         (246)2=(4.2×104R2)3×(ME4ME)

         42×4=(4.2×104R2)3R2=1.05×104 km