Gravitational force acts on a particle due to fixed uniform solid sphere. Neglect other forces. Then particle

Options

A. always moves normal to the radial direction.
B. always moves in the radial direction only.
C. always moves in circular orbit.
D. experiences a force directed along the radial direction only.

Answer

To solve the problem regarding the gravitational force acting on a particle due to a fixed uniform solid sphere, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the System**:
- We have a fixed uniform solid sphere with a particle located outside the sphere. The gravitational force acts on the particle due to the mass of the sphere.

2. **Identifying the Gravitational Force**:
- The gravitational force \( F_g \) acting on the particle (mass \( m \)) due to the sphere (mass \( M \)) can be expressed using Newton's law of gravitation:
\[ F_g = \frac{G M m}{r^2} \]
where \( G \) is the gravitational constant, \( M \) is the mass of the sphere, \( m \) is the mass of the particle, and \( r \) is the distance between the center of the sphere and the particle.

3. **Direction of the Gravitational Force**:
- The gravitational force acts radially inward, meaning it pulls the particle towards the center of the sphere. This is a crucial point because it determines the motion of the particle.

4. **Analyzing the Motion of the Particle**:
- If the particle has no initial velocity, it will simply accelerate towards the sphere due to the gravitational attraction. If it had an initial velocity, we would need to analyze the components of that velocity to determine the path.

5. **Conclusion on Motion**:
- Since the gravitational force is directed radially inward, if the particle has no initial tangential velocity, it will move directly towards the center of the sphere along the radial line. If it had a tangential component, it could move in a circular orbit, but this is not the case here.

6. **Final Statement**:
- The correct interpretation of the motion of the particle is that it experiences a force directed along the radial direction only, which confirms that the particle will move towards the center of the sphere.

### Answer:
The particle experiences a force directed along the radial direction only.