Question

The following figure shows two shells of masses $m_1$ and $m_2$. The shells are concentric. At which point, a particle of mass $m$ shall experience zero force?

• A. $\text{A}$
• B. $\text{B}$
• C. $\text{C}$
• D. $\text{D}$

Answer 1

The correct option is D $\text{D}$

As we know that the gravitational field inside a spherical shell is zero.

Point $\text{D}$ is an internal point for both $m_1$ and $m_2$. Hence, the gravitational field at point $\text{D}$ will be zero.

So, the force experienced by the particle at point $\text{D}$ will be zero.

But the particle at point $\text{C}$ will experience force due to $m_2$ only because it lies inside the $m_1$ and outside the $m_2$.

Particles at points $\text{B}$ and $\text{A}$ will experience the force due to both masses $m_1$ and $m_2$ as they lie outside the shells.

Therefore, option $\left(d\right)$ is correct.

$\text{Key Concept:}$ The gravitational field inside a spherical shell is zero.