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Question diagram

In the above spring block arrangements, the time period is asked for $K_1=2K$ left spring and $K_2=K$ right spring.

Now at equilibrium, $$T=K_2x=Kx=mg$$ $$2T=K_1y=2Ky=2mg \implies x=y$$ for movable pulley.

How does conservation of mechanical energy hold in spring block systems?

For slow release(no KE change), loss in PE of block is stored in springs. Since block moves by $2y+x=3x$ down
2y because of movable pulley and x because of right spring
Then $$mg(2y+x)=\frac{1}{2}K_1y^2+\frac{1}{2}K_2x^2$$ Using my initial force balance equation, $$mg(3x)=mg(x)+\frac{mg(x)}{2}$$

Therefore energy is not conserved. What happened to the rest of it ? What did I do wrong?

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  • $\begingroup$ "For slow release(no KE change), loss in PE of block is stored in springs". Can you justify this assumption with some citation? $\endgroup$
    – AJN
    Commented Dec 8, 2023 at 12:35
  • $\begingroup$ Can you use force equilibrium after you move weight into another position? I think there is only one static equilibrium, other ones will be dynamic and the weight will have to accelerate. Or you can hold it there using external force. $\endgroup$ Commented Dec 8, 2023 at 18:02

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