A spring 150-cm long extends to a length of 155 cm when it supports a load of 55 N. Determine the spring constant. F = kx x1= 1.5 m x2= 1.55 m F = 55 N k = ? Now, "x" in F = kx is x2-x1, right? So the formula would be 55 = .05k? Sorry, I know this is simple, I just am having a momentary lapse.