Answer:
the affirmation is False
Step-by-step explanation:
This expression can be analyzed using Newton's laws and specifically Newton's third law that establishes that the force that one body (1) exerts on another body (2) is of the same magnitude as the force exerted by the second body on the first, but in the opposite direction.
Based on this law, the body applies a force to the box and the box reacts with a force on the string of equal magnitude, no matter if it is moving or not, but it contrary direction,
in view of this explanation the affirmation is False