a long spring is stretched by 4 cm, and its potential energy is 80 J. If the spring is compressed by 2 cm, its potential energy will be

Options

A. 320 J
B. 20 J
C. 120 J
D. 60 J

Answer

B

Explanation

`(E_(2))/(E_(1)) =(F_(2))/(F_(1)) xx (l_(2))/(l_(1)) =(yAl_(2))/(yAl_(1)) xx (L)/(L) xx (l_(2))/(l_(1)) =(l_(2)^(2))/(l_(1)^(2))`
`therefore E_(2) =(4 xx 80)/(16) = 20J. `