Consider the following statements. Work is not done, when:
1. a man is walking on a horizontal road.
2. a man is climbing up a hill.
3. a man with a load on his head is walking on a horizontal road.
4. moon is revolving round the earth. Which of the statements given above are correct?

Options

A. 1 and 3 only
B. 1 and 4 only
C. 2, 3 and4
D. 1, 3 and 4

Explanation

To determine which statements are correct regarding when work is not done, we need to analyze each statement based on the definition of work in physics. Work (W) is defined as the product of force (F) and displacement (s) in the direction of the force, mathematically expressed as:

\[ W = F \cdot s = F \cdot s \cdot \cos(\theta) \]

where \(\theta\) is the angle between the force and the direction of displacement.

### Step-by-step Solution:

1. **Statement 1: A man is walking on a horizontal road.**
- In this case, the force exerted by the man is vertical (his weight), while the displacement is horizontal. Therefore, the angle \(\theta\) between the force and displacement is 90 degrees.
- Using the formula:
\[ W = F \cdot s \cdot \cos(90^\circ) = F \cdot s \cdot 0 = 0 \]
- **Conclusion**: Work is not done. (This statement is correct.)

2. **Statement 2: A man is climbing up a hill.**
- Here, both the force (the man’s effort against gravity) and the displacement (up the hill) are in the same direction. Thus, \(\theta\) is 0 degrees.
- Using the formula:
\[ W = F \cdot s \cdot \cos(0^\circ) = F \cdot s \cdot 1 \]
- **Conclusion**: Work is done. (This statement is incorrect.)

3. **Statement 3: A man with a load on his head is walking on a horizontal road.**
- Similar to the first statement, the force (weight of the load) acts vertically downward while the displacement is horizontal. Thus, \(\theta\) is again 90 degrees.
- Using the formula:
\[ W = F \cdot s \cdot \cos(90^\circ) = F \cdot s \cdot 0 = 0 \]
- **Conclusion**: Work is not done. (This statement is correct.)

4. **Statement 4: The moon is revolving around the earth.**
- The gravitational force acts towards the Earth, while the moon's displacement is tangential to its orbit. The angle \(\theta\) between the gravitational force and the displacement is 90 degrees.
- Using the formula:
\[ W = F \cdot s \cdot \cos(90^\circ) = F \cdot s \cdot 0 = 0 \]
- **Conclusion**: Work is not done. (This statement is correct.)

### Final Answer:
The correct statements where work is not done are **1, 3, and 4**.