NDA2024General AbilityGeneral ScienceActual
A spherical shell of outer radius R and inner radius R / 2 contains a solid sphere of radius R / 2 (see figure). The density of the material of the solid sphere is and that of the shell is / 2 . What is the average mass density of the larger sphere thus formed?
Options
- A3 / 4
- B9 / 16
- C7 / 8
- D5 / 8
Correct answer
B. 9 / 16
Step-by-step solution
aligned & Average density = Total mass Total volume & = ₁ V₁+ ₂ V₂ V & = 4 3 ( R 2 )^3+ 2 [ 4 3 R ^3- 4 3 ( R 2 )^3 ] 4 3 R ^3 & = 4 3 R ^3 8 + 2 [ 4 3 R ^3- 4 3 R ^3 8 ] 4 3 R ^3 & = 8 + 2 [1- 1 8 ] & = 8 + 2 [ 7 8 ] & = 8 + 7 16 & = 2 +7 16 = 9 16 . aligned