A spring with a mass attached to it is stretched from the rest position of 20 cm to the position of 87 cm. If the spring constant of this spring is 1729 N/m, what is the potential energy stored in this spring? 561.29 J
120.97 J
388.07 J
254.79 J

C) 388.07

Explanation:

It is a spring therefore, there must be Elastic potential energy. Now what is the formula for elastic potential energy? It is 1/2 *k *x^2

K=spring constant

x= displacement  

1/2=.5 (hate fractions)

Now, Displacement simply means (how much was it moved?) So, that means subtract.

87-20= 67   x=67

Next, do x^2 (so you don't make a mistake by squaring everything :)  )

67*67=4,489

NOW, do

.5*1729*4,489=3,880,740.5

Now convert to Joules, I just did 3,880,740.5  / 10^3 = 3880.745

round to 3880.7 J  

                                                                ~There you go loves !

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

i would say