Is the textbook wrong or am I?

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Homework Help Overview

The discussion revolves around a problem involving a vertical spring with a given spring constant and compression, tasked with determining the upward speed imparted to a ball upon release. The original poster and others are comparing their calculated results with the textbook's answer.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are using the conservation of energy principle to calculate the speed of the ball, questioning the accuracy of their calculations compared to the textbook. There is a focus on the interpretation of variables and the setup of the energy equation.

Discussion Status

Some participants express confidence in their calculations, while others suggest that the textbook's answer may be correct. There is an ongoing examination of the assumptions made regarding the variables involved in the energy conservation equation.

Contextual Notes

Participants are discussing the implications of gravitational effects on the calculations and the potential confusion arising from the use of different variable names for vertical distances.

drewdiddy
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Homework Statement



A vertical spring (ignore its mass), whose spring constant is 875 N/m is attached to a table and is compressed down by .160 m. (a) What upward speed can it give to a .380 kg ball when released?


Homework Equations



Conservation of Energy using 1/2 k x^2 for Uspring.

The Attempt at a Solution



I get 7.68 m/s for the velocity and the book gets 7.47 m/s. Wanted to see who was right and if I'm doing something wrong.
 
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drewdiddy said:

Homework Statement



A vertical spring (ignore its mass), whose spring constant is 875 N/m is attached to a table and is compressed down by .160 m. (a) What upward speed can it give to a .380 kg ball when released?


Homework Equations



Conservation of Energy using 1/2 k x^2 for Uspring.

The Attempt at a Solution



I get 7.68 m/s for the velocity and the book gets 7.47 m/s. Wanted to see who was right and if I'm doing something wrong.

"Upward" also means against gravity. You should also figure as an adjustment the m*g*h over the displacement of the acceleration.
 
So you're saying you got the book's answer?

I used the conservation of energy subbing values for spring and taking into account y=0 when crossing the original spring length. I'm quite sure I have the right answer and the book's is wrong but I just want to verify.
 
drewdiddy said:
So you're saying you got the book's answer?

I used the conservation of energy subbing values for spring and taking into account y=0 when crossing the original spring length. I'm quite sure I have the right answer and the book's is wrong but I just want to verify.

I'm just saying that

mv2/2 = kx2/2 - m*g*x
 
Last edited:
You are wrong, your book is right, Pion is right: (except I would not use both "h" and "x", there is only one vertical distance in the problem)
 
borgwal said:
You are wrong, your book is right, Pion is right: (except I would not use both "h" and "x", there is only one vertical distance in the problem)

Thanks for the catch. Of course h and x are the same.

I edited the previous post to be correct now.
 

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