Work done by force of static friction .

Options

A. can be positive
B. can be negative
C. can be zero
D. All of these

Explanation

### Step-by-Step Solution:

1. **Understanding Static Friction**:
- Static friction is the force that prevents an object from moving when a force is applied. It acts when an external force is trying to move a stationary object but the object does not move.

2. **Identifying the Conditions**:
- For static friction to act, the applied force must be less than or equal to the maximum static friction force, which is given by the equation:
\[ F_s \leq \mu_s N \]
where \( \mu_s \) is the coefficient of static friction and \( N \) is the normal force.

3. **Analyzing Work Done**:
- Work done by a force is defined as:
\[ W = F \cdot d \cdot \cos(\theta) \]
where \( F \) is the force, \( d \) is the displacement, and \( \theta \) is the angle between the force and the displacement direction.

4. **Considering the Displacement**:
- In the case of static friction, if the object remains at rest (which is the case when static friction is in action), the displacement \( d \) is zero.

5. **Calculating Work Done**:
- Since the displacement is zero, the work done by static friction can be calculated as:
\[ W = F_s \cdot 0 \cdot \cos(\theta) = 0 \]
- Therefore, the work done by the force of static friction is zero.

6. **Conclusion**:
- The work done by the force of static friction can only be zero when the object does not move.

### Final Answer:
The work done by the force of static friction is **zero**.

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