Two concentric spherical shells have masses `m_(1) and m_(2)` and radii `r_(1) and r_(2) (r_(2) gt r_(1))`. What is the force exerted by this system on a particle of mass `m_(3)`. If it is placed at a distance `r(r_(1) lt r lt r_(2))` from the centre ?

Explanation

To solve the problem, we need to determine the gravitational force exerted by two concentric spherical shells on a particle of mass \( m_3 \) placed at a distance \( r \) from the center, where \( r_1 < r < r_2 \).

### Step-by-Step Solution:

1. **Understanding the Setup**:
We have two spherical shells:
- Inner shell with mass \( m_1 \) and radius \( r_1 \).
- Outer shell with mass \( m_2 \) and radius \( r_2 \).
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