Question

Imagine a planet having the same density as that of the earth but radius is three times the radius of the earth. If acceleration due to gravity on the surface of the earth is g and that of the said planet is g' then

• A. g' = g/9
• B. g' = 9g
• C. g' = g/27
• D. g' = 3g

Answer 1

Answer: (D)

g' = 3g

Answer 2

g = $\frac { \mathrm { GM } } { \mathrm { R } ^ { 2 } } = \frac { \mathrm { G } ( 4 / 3 ) \pi \mathrm { R } ^ { 3 } \rho } { \mathrm { R } ^ { 2 } } = \mathrm { G } \frac { 4 } { 3 } \pi \mathrm { R } \rho$

Q R_Planet = 3R Hence g' = 3g