This isn't really a homework problem, but I've been going over these Yale problem sets for physics 200 (http://oyc.yale.edu/physics/fundamentals-of-physics/content/resources/problem_set_3.pdf" [Broken]), and I'm having trouble with one of the questions. 1. The problem statement, all variables and given/known data Two springs have the same unstretched length but different spring constants k1 and k2 . Find the effective force constant ke if they are connected in series and in parallel. (To ¯nd ke, imagine stretching the combination by an amount x and keeping track of the force needed.) 2. Relevant equations f = ma fs = -kx Pupil = awesome 3. The attempt at a solution So I figured the parallel spring constant out fairly easily, but I'm having trouble with the series one. The way I imagined it is we tie spring with constant [tex]k_1[/tex] to the wall, and tie spring with constant [tex]k_2[/tex] to spring with constant [tex]k_1[/tex], and finally pull [tex]k_1[/tex] by some amount A. Spring with [tex]k_1[/tex] will stretch by some amount A1 and spring with [tex]k_2[/tex] will stretch by some amount [tex]A_2[/tex]. Summing up, we have [tex]k_2A_2 + k_1A_1 = F[/tex]. The problem is I don't know what [tex]A_1[/tex] and [tex]A_2[/tex] are. I know the springs won't stretch the same amount, so I'm stuck with this ugly expression. Help me get unstuck (don't tempt me to look at the answers)! Thanks! EDIT: The title was supposed to be Spring Constant in Series...Don't know what happened.