2) A 20 kg mass moving at a speed of 3 m/s is stopped by a constant force of 15 N. How many seconds must the force act on the mass to stop it? 0.20 s O 1.3s O 5.0 s O 4.0 s

Take the object's starting direction of motion to be the positive direction, so that a stopping force acts in the opposite direction. By Newton's second law, the object undergoes an acceleration a such that

-15 N = (20 kg) a

Solve for a :

a = - (15 N) / (20 kg) = -0.75 m/s²

The object's velocity v at time t is then given by

v = 3 m/s + (-0.75 m/s²) t

so the time it takes for the object to slow to a rest is

0 = 3 m/s + (-0.75 m/s²) t

t = (3 m/s) / (0.75 m/s²) = 4.0 s

it would be kevlar ^^

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