Question

The height of the point vertically above the earth's surface, at which acceleration due to gravity becomes 1% of its value at the surface is (Radius of the earth = R)

• A. 8R
• B. 9R
• C. 10 R
• D. 20R

Answer 1

Answer: (B)

9R

Answer 2

Acceleration due to gravity at height is given by

$g ^ { \prime } = g \left( \frac { R } { R + h } \right) ^ { 2 }$

$\Rightarrow \frac { g } { 100 } = g \left( \frac { R } { R + h } \right) ^ { 2 }$

$\Rightarrow \frac { R } { R + h } = \frac { 1 } { 10 }$ $\Rightarrow h = 9 R$.