Acrab fisherman has built a crab trap out of plastic pipe and wire mesh. the overall mass and volume of the trap are 5.59 kg and 6,213 cm^3, respectively. to catch crab, the trap must sink to the ocean floor. the fisherman has several lead weights to add to the trap to ensure it sinks. if sea water has a density of 1,021 kg/m^3 , and each lead weight has mass of 113.4 g and volume of 10.0cm^3, what is the minimum number of weights the fisherman must add so that the trap sinks to the ocean floor?

To develop this problem it is necessary to apply the concepts related to the force of gravity, and the force expressed in terms of density and volume, by definition we know that,

Where,

Density

V = Volume

In addition we also know that by Newton's second law the weight can be defined as

For balance to exist, the Bouyancy force is equal to the weight, therefore

We know that the total weight is conditioned at 5.59 Kg plus the number of objects in Kilograms, that is

We know that the Volume is the equivalent of plus the volume of each weight of , so,

Replacing with our values we have that

Therefore the minimum number of weights is 8.

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