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 !

the device is called “ rocket engine”

when heated, the valance electrons increased their speed and transferred the heat from electron to electron.   i just took the test.