Imagine a spring made of a material that is not very elastic, so that the spring force does not satisfy hooke’s law, but instead satisfies the equation f = −α x + β x3 , where α = 10 n/m and β = 850 n/m3. calculate the work done by the spring when it is stretched from its equilibrium position to 0.15 m past its equilibrium. answer in units of mj.