Is it must that there is some mass at the center of mass?

Define centre of mass.

What is the mass of the earth?

What is molar mass ?

What is atomic mass unit?

The S.I unit of mass is

Is centre of mass a reality?

A positron has same mass as:

A Merry-go-round made of a ring-like platform of radius R and mass M is revolving with angular speed omega . A person of mass M is standing on it. At one instant, the person jumps off the round radially away from the center of the round (as seen from the center of the round (as seen from the round). The speed of the round afterwards is