Q.

A light planet is revolving around a massive star in a circular orbit of radius R with a period of revolution T. If the force of attraction between planet and star is proportional to R-3/2 then choose the correct option            [2024]

1 T2∝R5/2  
2 T2∝R7/2  
3 T2∝R3/2  
4 T2∝R3  

Ans.

(1) 

       ∵ F∝1R3/2 or F=KR3/2

         Gravitational force provides centripetal force.

         KR3/2=mω2R

           ω2=KmR5/2

           (2πT)2=KmR5/2⇒T2

            =4π2mR5/2K⇒T2∝R5/2