Explanation:

Definition of Moment Axis:
The moment axis is the axis that is perpendicular to the plane of the force and the distance. It is a line about which a force tends to rotate an object.

True Statement:
The statement that the moment axis is in the direction perpendicular to the plane of the force and the distance is true. This is because the moment or torque is a vector quantity that is calculated as the cross product of the force and the distance from the point of rotation. The direction of the moment axis is determined by the right-hand rule, where the thumb points in the direction of the force, the fingers point in the direction of the distance, and the moment axis is perpendicular to the plane formed by the force and the distance.

Explanation of the Direction:
When a force is applied to an object at a certain distance from a pivot point, the moment or torque produced is in the direction perpendicular to the plane formed by the force and the distance. This is because the force creates a tendency to rotate the object around the pivot point, and the direction of this rotation is perpendicular to the force and distance.

Importance in Mechanics:
Understanding the direction of the moment axis is crucial in mechanics, as it helps in analyzing the rotational motion of objects and determining the equilibrium conditions. By knowing the direction of the moment axis, engineers and designers can predict how forces will affect the rotation of structures and machinery.

Therefore, the statement that the moment axis is in the direction perpendicular to the plane of the force and the distance is true, and it plays a significant role in the study of mechanics and engineering.