Paheli moves on a straight road from point A to point C. She takes 20 minutes to cover a certain distance AB and 30 minutes to cover the rest of distance BC. She then turns back and takes 30 minutes to cover the distance CB and 20 minutes to cover the rest of the distance to her starting point. She makes 5 rounds on the road the same way. Paheli concludes that her motion is

Options

A. only rectilinear motion.
B. only periodic motion.
C. rectilinear and periodic both.
D. neither rectilinear nor periodic.

Answer

To determine the type of motion Paheli is experiencing, we can break down her journey step by step.

### Step-by-Step Solution:

1. **Understanding the Journey:**
- Paheli starts at point A and moves to point C.
- She first travels from A to B, taking 20 minutes.
- Then, she travels from B to C, taking 30 minutes.

2. **Returning Journey:**
- After reaching C, she turns back.
- She travels from C to B, taking 30 minutes.
- Then, she travels from B back to A, taking 20 minutes.

3. **Total Time for One Round:**
- The total time taken for one complete round (A to C and back to A) is:
- A to B: 20 minutes
- B to C: 30 minutes
- C to B: 30 minutes
- B to A: 20 minutes
- Total time for one round = 20 + 30 + 30 + 20 = 100 minutes.

4. **Multiple Rounds:**
- Paheli makes 5 rounds in total.
- Therefore, the total time for 5 rounds = 5 * 100 = 500 minutes.

5. **Type of Motion:**
- The motion is along a straight path (from A to C and back), which is known as **rectilinear motion**.
- Since she returns to her starting point (A) after completing each round, her motion is also **periodic** because it repeats after a fixed interval of time.

### Conclusion:
Paheli's motion is both **rectilinear** and **periodic**.