Initial angular velocity of a circular disc of mass $$M$$ is $${\omega _1}.$$ Then two small spheres of mass $$m$$ are attached gently to diametrically opposite points on the edge of the disc. What is the final angular velocity of the disc?

The escape velocity of a body depends upon mass as

Which of the following is more close to a black body?

The kinetic energy needed to project a body of mass $$m$$ from the earth surface (radius $$R$$) to infinity is