Final answer:
The correct answer is A. Mass, time, and speed, because these are scalar quantities that are fully described by their magnitude only, without a need for direction.
Step-by-step explanation:
The question asks which of the following physical quantities is only scalar. Scalar quantities are those that can be fully described by a magnitude only and do not possess a direction. From the given options, mass, time, and speed are scalar quantities, considering they do not require direction in order to be fully described. On the other hand, force, acceleration, velocity, and weight are vector quantities because they each have both magnitude and direction.
Therefore, the correct answer to which of the following physical quantities is only scalar is A. Mass, time, and speed. To elaborate, mass is a measure of the amount of matter in an object, time refers to the duration of an event, and speed is the rate at which an object covers distance. None of these requires direction for their description. For instance, Newton's second law relates force, mass, and acceleration, showing that force is indeed a vector quantity as it arises from mass being accelerated in a certain direction. Additionally, centripetal force is impacted by mass, speed, and the radius of the curvature, again confirming that force is related to directional quantities.