Energy conservation of a light spring

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Homework Help Overview

The problem involves a light spring fixed at the bottom of a vertical tube, with a ball released from a height above the spring. The discussion centers around the energy conservation principles related to the ball's motion and the spring's compression, particularly in the context of gravitational potential energy and elastic potential energy as described by Hooke's law.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the implications of smooth contact surfaces on energy conservation and question why the ball eventually comes to rest despite the conservation of energy. There is also debate regarding the independence of spring compression from the initial height of the ball.

Discussion Status

The discussion is ongoing, with participants exploring various interpretations of energy dissipation and the relationship between gravitational potential energy and spring compression. Some guidance has been offered regarding the balance of forces when the ball comes to rest on the spring.

Contextual Notes

Participants are considering the effects of internal friction within the spring and the implications of the initial height on energy conservation. There is a focus on the assumptions made regarding energy loss and the nature of the forces at play.

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Homework Statement



A light spring is fixed to the bottom of a vertical tube.A ball is released from rest at a height h above the upper end of the spring as shown.After rebounding several times the ball eventually comes to rest and stay on top of the spring.Assume all contact surfaces are smooth and the spring obeys Hooke's law throughout.Which of the following statement is/are true?

(1)The compression of the spring is proportional to the mass of the ball.
(2)The compression of the spring is independent of the height h.
(3)The gravitational potential energy lost by the ball is equal to the strain energy stored in the spring.

Homework Equations


The Attempt at a Solution


The question state that the contact surface is smooth so energy cannot lose because of friction.So why the the ball eventually stop as the energy in the system is conserve?
And I would like to know why (2) is correct.The value of h determine the gravitational potential energy before releasing the ball,so the maximum potential energy stored in the spring depends on h.
 

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Some of the energy is dissipated inside the spring, because of internal friction. As the spring compresses and releases, its particles move with respect to each other and their motion transforms to internal energy (heat).

ehild
 
ehild said:
Some of the energy is dissipated inside the spring, because of internal friction. As the spring compresses and releases, its particles move with respect to each other and their motion transforms to internal energy (heat).

ehild

Thanks.
And I would like to ask why the compression of the spring is independent of the height h.
As 1/2kx2=mgh,the compression of the spring depends on h.
 
But energy is lost. The ball is in rest on the top of the spring, in equilibrium, and it "forgot" from what height it had fallen down initially. The opposite forces, gravity and spring force balance each other: mg=kx.

ehild
 
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