In an oscillations exercise there is a spring attached to another spring, attached to a block.
Long story short: I have to find the global $k$. In the solutions it says: "Because the springs are massless, they act similar to a rope under tension, and the same force $F$ is exerted by each spring."
I don't really understand how the springs being massless, is an argument for saying that they exert the same force (being the global force) upon the block.
Anyone care to elaborate?