Question

Presuming earth to be a uniform sphere, a scientist A goes deep inside a mine and another scientist B goes high in a balloon above earth surface. The intensity of gravitational field

• A. decreases when measured by A and increases when measure by B.
• B. decreases when measured by B and increases when measured by A.
• C. decreases when measured by both.
• D. remains constant when measured by both.

Answer 1

Answer: (C)

decreases when measured by both.

Going inside, the mass is proportional to $r^3$ while the gravitational field varies with distance as $r^{-2}$. Hence, effectively, gravitational field is proportional to $r$ which decreases as one moves inside.

On moving above the earth's surface, the mass remains constant but the gravitational field varies with distance as $r^{-2}$ and hence it decreases as $r$ increases.

Thus, in both the cases, gravitational field decreases. In fact, the gravitational field is maximum at the surface of the earth.

Answer is option C.