1. The problem statement, all variables and given/known data The spring of a dynamo-meter grows 20cm when one suspends a 4N on weight. What is the potential energy of the spring when one suspends a weight of 12N? 2. Relevant equations Ue = 1/2*k*r2 Ug= m*g*h 3. The attempt at a solution so to find k I do this step. 1/2*k*0.22 = 4*0.2 k=40N/M Now that I have k I can find the potential energy of the spring with 12N 1/2*40*r2 =12*r I find r to be 0.6 now I do 12*0.6 = 7.2J to fnd the potential energy of the spring. The real answer is 3.6J but I cant figure out how to get this.