- #36

CAF123

Gold Member

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If downwards is positive, shouldn't that be -(-k(L-a))? So this means that L is the extension of the spring from a. This is clear from your diagram.ehild said:See picture. The ceiling is the zero of coordinate y and downward is the positive direction. The top of the spring is at x=csin(nt). The length of the spring is L. so y=x+L.

For he mass m, [itex]m\ddot {y}=mg-k(L-a)\rightarrow \ddot {x} +\ddot L =g-\frac{k}{m}(L-a)[/itex]

Many thanks.

Where was it that I was going wrong? Was I too concentrated with the displacement of the bottom mass?