(a). By the inertia, it's difficult to stop heavier mass than lighter mass.
As, moment of inertia is directly proportional to the mass of the body.
Thus, more force is required to stop the boy with heavier mass than lighter mass.
The problem statement for the given case is,
The time taken by the heavier body to stop swinging is more than the lighter body, then what is the impact of weight on the time period of the swing?