1. The problem statement, all variables and given/known data 2. Relevant equations F=m*a 3. The attempt at a solution Don't worry it not a homework question of mine. I was just trying to solve some questions (on my own) that I know I have difficulty with to get better at it. Especially with springs I can get confused, so I thought I would try that. With this question I got stuck and I know that it was because I set the unstretched length as when the spring went a distance 'd' back, but of course he is only at equilibrium then and not unstretched then. But still I don't get the answer. They talk about that if y=d then N=0, but to me that does not seem right. y(equilibrium) + d, is the position he would be at when you press it down measured from the unstretched position? As I see it they saying, at the position the Block A is when it is being pushed down and released from rest, at that point there is no Fn working on it. Which would be silly. N=0 should be the point when the string is in unstretched position, since at that moment Block A and Pan B should seperate? So N=0 when F(spring)= 0= k*s, so when s=0.