A body is under the action of two equal and oppositely directed forces and the body is rotating with constant non-zero angular acceleration. Which of the following cannot be the separation between the lines of action of the forces ?

Options

A. 1 m
B. 0.4 m
C. 0.25 m
D. zero

Explanation

To solve the problem, we need to analyze the situation where a body is subjected to two equal and opposite forces while rotating with a constant non-zero angular acceleration.

### Step-by-step Solution:

1. **Understanding Forces**: We have two equal and opposite forces acting on the body. Let's denote these forces as \( F_1 \) and \( F_2 \). Since they are equal and opposite, they will not cause any translational motion, but they can create a torque about the center of mass of the body.

2. **Torque Calculation**: The torque (\( \tau \)) produced by a force is given by the formula:
\[ \tau = r \times F \]
where \( r \) is the distance from the pivot point (or center of mass) to the line of action of the force, and \( F \) is the magnitude of the force.

3. **Condition for Angular Acceleration**: For the body to have a constant non-zero angular acceleration, there must be a net torque acting on it. This means that the distance \( r \) (the separation between the lines of action of the two forces) must be non-zero.

4. **Analyzing the Options**:
- If the separation \( r = 0 \), then both forces act along the same line, and the torque produced by each force will cancel each other out, resulting in a net torque of zero. This would mean that there is no angular acceleration, which contradicts the given condition of constant non-zero angular acceleration.
- Therefore, the separation cannot be zero.

5. **Conclusion**: The only scenario that cannot occur while the body is rotating with a constant non-zero angular acceleration is when the separation between the lines of action of the forces is zero. Thus, the answer to the question is that the separation cannot be \( 0 \).

### Final Answer:
The separation between the lines of action of the forces cannot be \( 0 \).