Q.

Applying the principle of homogeneity of dimensions, determine which one is correct, where T is time period, G is gravitational constant, M is mass, r is radius of orbit.                                                      [2024]

1 T2=4π2r3GM  
2 T2=4π2r2GM  
3 T2=4π2r3  
4 T2=4π2rGM2  

Ans.

(1) 

     According to principle of homogeneity dimension of LHS should be equal to dimensions of RHS. [T2]=T2,

     Dimension of G is [M-1L3T-2]

      Now,

      (1) [4π2r3GM]=L3M-1L3T-2M1=T2

      (2) [4π2r2GM]=L2M-1L3T-2M1=L-1T2

      (3) [4π2r3]=L3

      (4) [4π2rGM2]=LM-1L3T-2M2=M-1L-2T2