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At equilibrium ,

Mg = N +V(rho-sigma)g

therefore , N = 0.2 newtons

U MEAN VARIABLE MASSES IN CASE OF THRUST (ROCKET)???

FOR SUCH QUESTIONS GENERALLY , U NEED 2 FIND RELATION BETWEEN MASSES AND TIME ( MAY BE VELOCITY , ACCELERATION ) WHICH ARE SUPPOSE TO VARY WITH TIME IN THE GIVEN PROBLEM , AFTER THIS , DIFFERENTIATE THE EQN. AND THATS UR RELATION !!

According to law of conservation of angular momentum :

I1w1 = I2w2 = constant

Where I1 & I2 are initial and final moment of inertia
w1 & w2 are initial and final angular velocity

therefore , I w = constant

point to be noted : when masses(particles ) are close to axis of rotation , moment of inertia is less while its more when masses are away from axis of rotation . Therefore, as the melted water moves away from axis, final moment of inertia increases !!!

Now from above mentioned equation , when I increases , ?w? decreases (inverse proportion)

Also , when w(angular velocity) decreases time period ?T? increases according to below relation

w = (2 ? )÷T

What ur sir said is exactly right , iwould like to add something to this .

when u take circular cardboard and pass a rod through its c.m(centre of mass)

when u rotate the cardboard , will rotate smooth as ever, but if you attach some blocks at the circumference and rotate, this time the angular velocity will be different from earlier one .

3. it will effect becoz , the axis of rotation will still be equidistant from the equatorial circumference but amount amount of masswill change at the poles

remember , angular velcity depend on :

1. distribution of particle(masses) around the axis of rotation

2.position of axis

1. Definitely,not !! becoz according to law of conservation of momentum , every time the rotating body comes in contact with the rough surface , an impulse acts on the surface , so torque is continuously acting and therefore according to law of conservation of angular momentum , when torque acts angular momentum is not conserved