A planet moves faster at

Options

A. Aphelion
B. Perihelion
C. Focus
D. It travels with uniform speed

Answer

To solve the question regarding the speed of a planet at different points in its orbit, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Terms**:
- **Aphelion**: The point in the orbit of a planet where it is farthest from the Sun.
- **Perihelion**: The point in the orbit of a planet where it is closest to the Sun.
- **Phobos**: A moon of Mars, not relevant to this question.

2. **Conservation of Angular Momentum**:
- The angular momentum (L) of a planet in orbit is conserved. This can be expressed as:
\[ L = m \cdot v \cdot r \]
- Here, \(m\) is the mass of the planet, \(v\) is its orbital speed, and \(r\) is the distance from the Sun.

3. **Setting Up the Equation**:
- For two different points in the orbit (let's say perihelion and aphelion), we can write:
\[ m \cdot v_1 \cdot r_1 = m \cdot v_2 \cdot r_2 \]
- We can simplify this to:
\[ v_1 \cdot r_1 = v_2 \cdot r_2 \]

4. **Analyzing the Relationship**:
- Rearranging the equation gives:
\[ \frac{v_1}{v_2} = \frac{r_2}{r_1} \]
- This indicates that the speed \(v\) is inversely proportional to the distance \(r\) from the Sun.

5. **Identifying Minimum and Maximum**:
- At perihelion, the distance \(r\) is at its minimum (let's denote it as \(r_{min}\)).
- At aphelion, the distance \(r\) is at its maximum (denote it as \(r_{max}\)).
- Since \(v\) is inversely proportional to \(r\), when \(r\) is minimum, \(v\) will be maximum.

6. **Conclusion**:
- Therefore, the planet moves faster at perihelion, where it is closest to the Sun.

### Final Answer:
The planet moves faster at **perihelion**.