Hi, I'm just training for the 2013 F=ma exam, and I took some old exams. I tried to do the 2012 exam, and could not figure out problem 21. Can anyone help me, please? 1. The problem statement, all variables and given/known data A spring system is set up as follows: a platform with weight 10 N is on top of two springs, each with a spring constant of 75 N/m. On top of the platform is a third spring with spring constant 75N/m. If a ball with weight of 5.0 N is fastened to the top of the third spring and then slowly lowered, by how much does the height of the spring system change? (A) 0.033 m (B) 0.067 m (C) 0.100 m (correct answer) (D) 0.133 m (E) 0.600 m 2. Relevant equations F=kx 3. The attempt at a solution The bottom springs act as one spring with K=150 N/m, thus will contract 0.033 m under the weight The top spring will compress 0.067 m under the weight so is it just addition...?