Calculating Spring Constant and Energy Conservation: How Fast Will the Bag Drop?

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Homework Help Overview

The problem involves a vertical spring system with a 3kg bag attached, requiring the calculation of the spring constant and the analysis of the bag's motion after dropping from a non-deformed position. The context includes concepts from mechanics, specifically energy conservation and oscillatory motion.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the calculation of the spring constant and the application of energy conservation principles to find the bag's velocity and displacement. Questions arise regarding the correct use of gravitational potential energy (GPE) and elastic potential energy (EPE) in the context of the problem.

Discussion Status

Some participants have provided guidance on the relationships between GPE, KE, and EPE, while others are exploring the implications of these relationships on the calculations. There is an ongoing examination of how to determine the GPE lost and its relevance to the bag's motion.

Contextual Notes

Participants are navigating uncertainties regarding the distance the bag drops and the assumptions made about energy conservation at different points in the motion. The problem's setup does not provide explicit values for certain variables, which affects the discussion.

MarieMarie94
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1. Problem Statement:
A vertical spring has one end attached to the ceiling and a 3kg bag attached to the other one. When the system is at rest, the spring is stretched by 40cm. 1) determine the spring constant. 2) Let the bag drop from a position in which the spring is not deformed. Using the conservation of energy law, find: how fast the bag is moving after it drops 40 cm, and how far down the bag will drop before starting to come back. Calculate and show the direction of the bag's acceleration when the bag is at the highest, lowest, and middle of the oscillation positions.

Homework Equations

:[/B]
K=mg/x
KE=1/2m(v^2)
GPE=mgh
EPE=1/2k(x^2)

3. Attempt at the Solution:
So I found a spring constant. I'm not sure if it's correct but I got, k=(3)(9.8)/(.4)= 73.5 N/m. I ran into problems with the rest though. For finding the velocity of the bag dropping 40cm, I did GPE=KE+EPE but I'm not sure if that's right. As for the farthest distance the bag would drop and the acceleration, I wasn't exactly sure how to approach them.

Update: To find the velocity at 40cm, should it actually only be GPE=KE because we're treating the 40cm as our equilibrium? And then to find the farthest distance the bag would drop would it be GPE=EPE to find our displacement? Or am I completely wrong?
 
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MarieMarie94 said:
GPE=KE+EPE
GPE lost = KE gained + EPE gained, yes.
MarieMarie94 said:
to find the farthest distance the bag would drop would it be GPE=EPE to find our displacement
Yes, but what is the GPE lost in this case?
 
haruspex said:
Yes, but what is the GPE lost in this case?
Would it be (3)(9.8)(d) because we don't know the distance?
 
MarieMarie94 said:
Would it be (3)(9.8)(d) because we don't know the distance?
Right.
 

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