$A$ disc is rotating with an angular velocity $\omega$. $A$ child sits on it gently. Which of the following quantities will be conserved?

What does not change in the field of a central force?

$A$ uniform disc of mass $M$ and radius $R$ is rotating about a horizontal axis passing through its centre with angular velocity $\omega$. $A$ piece of mass $m$ breaks from the disc and flies off vertically upwards. The angular speed of the disc will be

$A$ small mass attached to a string rotates on a frictionless table top as shown. If the tension in the string is increased by pulling the string,causing the radius of the circular motion to decrease by a factor of $2$,the kinetic energy of the mass will

The angular momentum of a system of particles is not conserved:

$A$ circular platform of moment of inertia $100 \ kg\ m^2$ with a boy of mass $20 \ kg$ standing at the centre completes one rotation in $10 \ s$. If he walks $2 \ m$ away from the centre along the radius,then one rotation (with respect to the ground) will be completed in $.... \ s$.