- #1
lion_
- 18
- 0
Homework Statement
A spring constant of ##3200 N/m## is initially streched until the elastic potential energy is ##1.44## J (##U=0## for no stretch). What is the change in elastic potential energy if the initial stretch is changed to (a) a stretch of ##2.0## cm, (b) a compression of ##2.0## cm, (c) a compression of ##4.0## cm.
Homework Equations
##\Delta U=U_f-U_i##
##U=\frac{1}{2}kx^2##
The Attempt at a Solution
(a) ##\Delta U=U_f-U_i=\frac{1}{2}(3200)(0.02)^2-1.44=-0.8 J##
(b) ##\Delta U=U_f-U_i=-\frac{1}{2}(3200)(0.02)^2-1.44=-2.08 J##
(c) ##\Delta U=U_f-U_i=-\frac{1}{2}(3200)(0.04)^2-1.44=-4J##
The first answer (a) is correct but the last 2 they get (b) ##-0.8J## and (c) ##1.1J## respectively. How?