Question

UNIVERSAL LAW OF GRAVITATION
A point mass m is placed inside a spherical shell of radius R and mass M at a distance $\frac{R}{2}$ from the centre of the shell. The gravitational force exerted by the shell on the point mass is:

• A. $\frac{GMm}{R^2}$
• B. $\frac{2GMm}{R^2}$
• C. zero
• D. $\frac{4GMm}{R^2}$

Answer 1

Answer: (C)

zero

The forces from all the parts of the shell will cancel each other at any point inside the shell. therefore net force will be zero

Use Gauss's Law directly, then you can simply think about it this way.

In the exact middle of the hollow shell, there will be a gravitational pull from every point on the shell, but each point will have a different direction.

In fact, for every point with a gravitational pull in one direction, there is a point on the exact opposite side of the ball with the same amount of pull but in the opposite direction.

Hence C option is correct