Final answer:
The velocity of a moving body in dynamic equilibrium is constant as the sum of the forces acting on the object is zero, which means there is no acceleration. This is consistent with Newton's first law of motion. Option a is the correct answer.
Step-by-step explanation:
When discussing the velocity of a moving body that is in dynamic equilibrium, it is essential to understand that dynamic equilibrium refers to a condition where the sum of the forces acting on an object is zero, but the object continues to move at a constant velocity. This means the object has no net force acting upon it and, therefore, no acceleration.
According to the principles of Newton's first law of motion, an object in motion will stay in motion with a constant velocity unless acted upon by a net external force. Therefore, if we're plotting a graph of displacement versus time for a body in dynamic equilibrium, it will be linear, indicating that the acceleration is zero (as option a in the reference material suggests).
In such a case, the correct answer to the question 'What can you say about the velocity of a moving body that is in dynamic equilibrium?' is: