Question

The distance of a geostationary satellite from the centre of earth (radius $R=6400km)$ is nearest to :

• A. 18 R
• B. 10 R
• C. 7 R
• D. 5 R

Answer 1

Answer: (C)

Geostationary satellites are positioned at an exact height above the earth (above $35600km$ ).
The distance of geostationary satellite from centre of earth is
$\left(R_e+35600\right)km=6400+35600$
$=42000km$
At this height they rotate around the earth with the same speed as the earth rotates around its axis.
So, its effect remains stationary above a point on earth.
$\therefore 42000=6400\times R$
$\Rightarrow R=\frac{42000}{6400}\approx 7R$.