A rigid body is said to be in partial equilibrium, when it is in

Options

A. a. translational equilibrium only
B. b. rotational equilibrium only
C. c. either (a) or (b)
D. d. neither (a) nor (b)

Explanation

To determine when a rigid body is said to be in partial equilibrium, we need to understand the concepts of translational and rotational equilibrium.

### Step-by-Step Solution:

1. **Understanding Complete Equilibrium**:
- A rigid body is in complete equilibrium when both the net force acting on it is zero and the net torque acting on it is also zero. This means that the body is not moving translationally (it is at rest or moving with constant velocity) and is not rotating (it has no angular acceleration).

2. **Defining Partial Equilibrium**:
- Partial equilibrium occurs when a rigid body is in equilibrium in one aspect (either translational or rotational) but not in both. This means that either the net force is zero while the net torque is not zero, or the net torque is zero while the net force is not zero.

3. **Analyzing the Options**:
- Option A: Translational equilibrium only - This implies that the net force is zero, but the body may still be rotating.
- Option B: Rotational equilibrium only - This implies that the net torque is zero, but the body may still be translating.
- Option C: Either A or B - This suggests that the body can be in either translational or rotational equilibrium, but not both.
- Option D: Neither A nor B - This suggests that the body is not in equilibrium in either aspect.

4. **Conclusion**:
- Since partial equilibrium can be defined as a state where a rigid body is in equilibrium in either translational or rotational aspects, the correct answer is **Option C: Either A or B**. This indicates that the body can be in one type of equilibrium while not being in the other.