A particle hanging from a spring stratches it by `1cm` at earth's surface. Radius of the earth is `6400 km`. At a place `800 km` above the earth's surface, the same particle will stretch the spring by

Options

A. `1cm`
B. `8cm`
C. `0.1cm`
D. `0.79cm`

Explanation

To solve the problem, we will use the relationship between the gravitational force acting on the particle and the stretch of the spring. The gravitational force depends on the distance from the center of the Earth, and as we move away from the Earth's surface, the gravitational force decreases.

### Step-by-Step Solution:

1. **Identify the initial conditions:**
- The particle stretches the spring by \( x_1 = 1 \, \text{cm} \) at the Earth's surface.
- The radius of the Earth, \( R = 6400 \, \text{km} = 6400000 \, \text{m} \).

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