Calculate total energy from potential at equilibrium point

EliteCodexer
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Homework Statement


A block of mass 0.25 kg is connected to a spring with spring constant 35 N/m. The block is oscillating on a frictionless horizontal surface. Its speed as it passes through its equilibrium position is 1.04 m/s. What's the total energy of the system?2. The attempt at a solution
Not sure how to find potential energy at equilibrium point given the speed as it passes through. I really just need someone to walk me through this problem.

Total Energy=Potential+Kinetic
 
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At the equilibrium point, there is no net force on the block. What does that tell you about the spring potential energy at that point?
 
there is none?
 
EliteCodexer said:
there is none?
That is correct. The spring is at its original unstretched length at that point. So what is the total energy at the equilibrium point in this example?
 
what about the kinetic energy though?
 
EliteCodexer said:
what about the kinetic energy though?
The total energy of the system is constant at at any point in time and equal to the sum of the kinetic and potential energies at any point in time. The total energy of the system at the equilibrium point is thus? and thus the total energy of the system at any point is?
 
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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