The motion of planets in the solar system in an example of conservation of

Options

A. mass
B. momentum
C. angular momentum
D. kinetic energy

Explanation

To solve the question regarding the motion of planets in the solar system and its relation to conservation principles, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the conservation principle that applies to the motion of planets in the solar system. We have four options: mass, momentum, angular momentum, and kinetic energy.

2. **Kepler's Laws of Planetary Motion**: Recall that Kepler's laws describe the motion of planets. Particularly, Kepler's second law states that a line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time. This implies that the areal velocity (area swept out per unit time) is constant.

3. **Areal Velocity and Angular Momentum**: The areal velocity can be expressed in terms of angular momentum (L) and mass (m) of the planet. The formula for areal velocity (dA/dt) is given by:
\[ \text{Areal Velocity} = \frac{L}{2m} \]
This indicates that if the areal velocity is constant, then angular momentum must also be conserved.

4. **Conservation of Angular Momentum**: Since the areal velocity remains constant as the planets orbit the Sun, we conclude that the angular momentum of the planets is conserved. This is because there are no external torques acting on the planets in their orbits around the Sun.

5. **Conclusion**: Based on the above reasoning, the motion of planets in the solar system is an example of the conservation of angular momentum. Therefore, the correct answer is option 3: angular momentum.

### Final Answer:
The motion of planets in the solar system is an example of conservation of **angular momentum**.