As a descending elevator approaches the correct floor, it slows to a stop with a constant acceleration of magnitude 1 ms21\,\dfrac{\text{m}}{\text{s}^2} 1 s 2 m 1, start fraction, start text, m, end text, divided by, start text, s, end text, squared, end fraction . The elevator descends 4.5 m4.5\,\text{m} 4.5m 4, point, 5, start text, m, end text while it is slowing. We want to find how many seconds the elevator takes to slow to a stop.

Explanation:

Given that,

The elevator slow to stop, this shows that it is decelerating and the final velocity is 0

v = 0m/s

Constant deceleration

a = -1m/s²

It is negative because it is deceleration

The distance the elevator descend is 4.5m

S=4.5m

Then, we want to find the time the elevator spent before stopping

Using the equation of motion

v = u + at

v² = u² + 2as

Where

v is final velocity

u Is initial velocity

a is the deceleration

s- is distance traveled

From here we can find the initial velocity of the elevator

v² = u² + 2as

0² = u² - 2 × 1 × 4.5

0 = u² - 9

u² = 9

u = √9

u = 3m/s

The initial speed is 3m/s

Then, to find the time taken, we can use the first equation

v = u + at

0 = 3 - 1 × t

0 = 3 - t

t = 3 seconds

The time taken before the elevator stop is 3 secs

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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