Auniform disk of mass 20.0 kg and radius 20.0 cm has an additional rim of mass 20.0 kg as well as four symmetrically placed masses, each of mass 1/4th of the mass of the disk, fastened at positions having position vectors (10.0 i + 10.0 j) cm, (10.0 i - 10.0 j) cm, (-10.0i - 10.0 j cm, (-10.0 i + 10.0 j) cm (with respect to the center of the disk). what is the moment of inertia of the whole unit about an axis perpendicular to the disk and passing through its center?

Explanation:

Moment of inertia of disc is given as

now we have

m = 20 kg

R = 20.0 cm = 0.20 m

now we have

Now the additional mass of 20 kg is placed on its rim so it will behave as a ring so moment of inertia of that part of the disc is

m = 20 kg

R = 20 cm = 0.20 m

Now four point masses each of the mass of one fourth of mass of disc is placed at four positions so moment of inertia of these four masses is given as

here we have

Now total moment of inertia of the system is given as

because growing process had stoped after 4-5 year

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia