Suppose you are in an elevator that is moving upward. as the elevator nears the floor at which you will get off, its speed slows down. during this time when the elevator is moving upward with decreasing speed, your weight will be

Less than your normal weight at rest

Explanation:

When the elevator is moving upwards with decreasing speed it means that the elevator is decelerating, thus the weight is lower than normal even though you are being pulled down with gravity acceleration.However, remember that your normal force is equal to your weight when the elevator is accelerating upwards,  you feel a little heavier than usual and a little litter if the elevator is accelerating downwards.

a and b sometimes have a positive value

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