1. The problem statement, all variables and given/known data A body with mass m start from repose and slide along a plane without friction. The plane forms an angle with the horizontal. After sliding a distance d unknown, the mass touches the extremity of a spring non compressed and non stretched with no mass. The mass slides a distance x until a momentary rest by the compression of the spring (of constant k). Find the initial separation d between the body and the extremity of the spring. 2. Relevant equations So first, I tried to translate this exercise from Portuguese, so if some words doesn't make sense, I'm sorry! The doubts I have is where to define the highness at zero. I tried to put z=0 at the moment when the mass compress the spring, in the momentary rest. Then I used conservation of energy and obtained the following result: 3. The attempt at a solution Energy A (when the mass start to slides): E=mg(d+x)sinβ Energy B (when the mass compress the spring): E=½kx^2 Considering that there's no friction E_A=E_B and I obtain that the distance d equals to: d=½kx(x-1) Is it right?