1. The problem statement, all variables and given/known data a .7 lb block rests on top of a .5 lb block supported by but not attached to a spring of constant 9 lb/ft. the upper block is suddenly removed. determine the maximum velocity reached by the .5 lb block. 2. Relevant equations 3. The attempt at a solution i have already solved the probelm. my question is, why is the expression for the force on the spring F = 1.2 - kx =>> 1.2 - 9x. i get the 1.2 part but im not understanding why its 1.2 minus 9x. im trying to understand this visually with arrows but its not quite working...pls help!