Initial and Final Energy problem

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The discussion revolves around a physics problem involving a 2.4 kg piece of wood sliding on a surface with both smooth and rough sections. The wood starts from rest at a height of 4.0 m and experiences kinetic friction on a 31 m horizontal stretch. For part a, the user proposes using the conservation of energy principle, equating potential gravitational energy to friction energy to find the distance d where the wood comes to rest. For part b, the user inquires whether the work-energy theorem can be applied despite the presence of friction. The conversation emphasizes the application of energy principles to solve for the motion and work done by friction.
YamiBustamante
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Homework Statement


[/B]
A 2.4 kg piece of wood slides on the surface shown in the figure . The curved sides are perfectly smooth, but the rough horizontal bottom is 31m long and has a kinetic friction coefficient of 0.27 with the wood. The piece of wood starts from rest 4.0m above the rough bottom.

a) Where will this wood eventually come to rest?

b) For the motion from the initial release until the piece of wood comes to rest, what is the total amount of work done by friction?

Homework Equations


E_k = (1/2)mv^2
E_f = mg(u_k)d
E_g = mgh

The Attempt at a Solution



I think I have an idea for part a but I'm not sure. Would this be correct?

Initial Energy = Final Energy
Potential Gravitational Energy = Friction Energy
mgh = Ugdm
(2.4kg)(9.8m/s^2)(4.0m) = 0.27(9.8m/s^2)(2.4kg)d
And then I figured that I would solved for d...
Would that be correct? And for part b would I use the work kinetic energy theorem even though it has friction?
 

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I think you got it.
 
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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