Question

A planet has twice the mass of earth and of identical size. What will be the height above the surface of the planet where its acceleration due to gravity reduces by 36% of its value on its surface?Ans-1600km

Answer 1

Gravity on surface g =  2GM/R square = 2 x 9.8 = 19.6 m/s square  

Where M is the mass of the earth and r is the radius of the earth 

H is the height where gravity is reduced by 36 percent of g 

 g' = g (1- 2h/r) 

= g – 36% of g 

= g - 36/100 g  

= 64/100 g 

g (1 - 2h/r) = 64/100 g 

1- 64/100 = 2h/R 

36/100 = 2h/R  

h = 18/100 R  

At the height equal to the 18% of R gravity is reduced by 36% of g.

Answer 2

Hope it helps you I got the answer as 1600km