Q.

Assuming the earth to be a sphere of uniform mass density, a body weighed 300 N on the surface of earth. How much it would weigh at R/4 depth under surface of earth                [2024]

1 300 N  
2 75 N  
3 225 N  
4 375 N  

Ans.

(3) 

      At surface: mgs=300Nm=300gs

       Gravitational field at R4 depth under surface, gd=gs[1-dR]

       gd=gs[1-R4R]=3gs4

      Weight at depth, Wd=m×gd=m×3gs4=34×300=225N