During a test experiment, the engineer finds an ideal very light spring has already been stretched 1.4m from its original length. He also finds that he needs to perform 100J of work to further stretch this spring an additional 1.5m. What is the value of the spring constant for this spring? 2. Relevant equations W = F*d F = -kx So I wrote out that F1 = -kx to stretch the spring the initial 1.4m and then to stretch it the additional 1.5m it would take: F2 +F1 = -2.9*k I also wrote out: F1 = -1.5k Then I used 100 = F2*1.5 so F2 = 66.67 although I'm not sure if you can use this equation for a spring Then 66.67 -1.5k = -2.9k and I tried solving for k but that didn't work so I'm not sure what else to try.