Engineering Why wasn’t gravity included in the potential energy for this problem?

SafiBTA
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Homework Statement
Derive the equation of motion using the principle of conservation of energy
Relevant Equations
T = ½ m ẋ² + ½ J₀ θ̇²

x = 4 r θ

U_spring = ½ k (4 r θ)²

(What’s confusing me is: shouldn’t there also be a gravitational potential term U_g = m g x ?)
I’m looking at the attached vibration problem. The solution in the manual includes the spring potential energy but does NOT include the gravitational potential energy of the hanging mass.

Can someone explain why gravitational potential energy is not included when deriving the equation of motion? I tried asking ChatGPT but kept going in circles and couldn't figure out.

Thanks!

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Thread 'Full bridge circuit with inductor and resistor'
The above is the circuit i am calculating the inductor current. During the positive half of the sine input D1 and D3 are conducting so the circuit becomes My calculations are as below Are the above equations ok? When transitioning from +Ve cycle to -Ve sine wave does the above equations still applicable? During the negative cycle the diodes D2 and D4 are conducting and the current direction is going into the inductor same as when diodes D1 and D3 are conducting. According to me the same...

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