A light spring is used to connect three objects a, B and C of M1, M2 and M3. How big is f when the stiffness coefficients of AB, K1 and BC are just separated from the ground? (1) How big is f when C is just separated from the ground? (2) how high does a rise at this time?

A light spring is used to connect three objects a, B and C of M1, M2 and M3. How big is f when the stiffness coefficients of AB, K1 and BC are just separated from the ground? (1) How big is f when C is just separated from the ground? (2) how high does a rise at this time?

1. Just off the ground means n = 0! At this time, for ABC as a whole, there is f = (M1 + M2 + m3) g P.S. the tension of the spring is internal force, which does not need to be considered with the integral method!
2. At this time, analyze C, FBC = M3G, analyze BC as a whole, Fab = (M2 + m3) g. at this time, calculate FBC and Fab instantaneously, then calculate the elongation of two springs, and then add their original length