This is for a vibrations course. A force F(t)=Focos(w*t) is applied to a point on a spring located 25% of its length from the fixed end (at the ceiling). I am trying to write out Newton's 2nd for the block. This requires that I find how much of F(t) is transmitted to the block. I am a little confused as to where to start. I am also confused as to why they labeled the different parts of the spring with different spring constants? (see figure below from solution) Why do different parts of the spring have different constants. Is k a function of length? Any ideas are appreciated.