The centre of mass of a two-particle system lies on the line joining them, closer to MCQ with Answer and Explanation

Explanation:
Magnetic force perpendicular to velocity, work zero, KE constant.

Explanation:
This is based on the conservation of angular momentum (L = Iω), where 'I' is the moment of inertia and 'ω' is angular velocity. When the boy extends his arms, mass moves further from the axis of rotation, increasing his moment of inertia (I). Since 'L' is conserved, an increase in 'I' must result in a decrease in angular velocity (ω).

Explanation:
Tension is towards centre, displacement is tangential (velocity). Force perpendicular to displacement, cos90°=0, work zero. Centripetal force does no work, doesn't change speed.