Deformation of Solids: Solving Question 18 from 9702_s13_qp_13

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Homework Help Overview

The discussion revolves around a question from a physics exam concerning the deformation of solids, specifically focusing on the relationships between force, length, area, and how these relate to scaled models versus full-size counterparts.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the relationships between dimensions, force, and area in the context of a scaled model. There are discussions about the proportionality of various quantities and how they affect the deformation of solids.

Discussion Status

Some participants have offered insights into the relationships between the model and full-size dimensions, while others are working through their understanding of the problem and seeking clarification on their reasoning. There is an ongoing exploration of the correct approach to the problem, with some participants expressing uncertainty about their calculations.

Contextual Notes

There are references to specific rules and expectations for problem-solving in the forum, as well as the importance of using proper templates for clarity. Participants are also navigating the challenge of understanding the implications of scaling in physical problems.

yan_plusheartz
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Homework Statement



Hey, I have problems solving this question. May I know how to solve this question. Somehow, the answer I got is to the power of negative. can someone show me the step by step solution to this question? (Question 18 from this paper) the link is below.
http://maxpapers.com/wp-content/uploads/2012/11/9702_s13_qp_13.pdf


Homework Equations


E = Fl / Ae


The Attempt at a Solution

 
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Hello Yan, and welcome to PF. There's a few rules here that are universally accepted -- and severely imposed.
One is to use the template. You did that in a smart way. Laziness can be a good quality in physics.
But you missed number 1 and number 3. The first error could have been avoided by rendering the problem instead of dumping the whole exam. The other is unforgivable, since it prevents helpers from helping you properly.

At first I thought I might help you a little by alleviating the stress that can accompany having to struggle at an exam. but the date tells me this is practicing. So we have the time, right? Let's use it effectively, both yours and that of potential helpers.

This is what I found at number 18 on a first attempt:

18 The formula for hydrostatic pressure is p = ρ gh.
Which equation, or principle of physics, is used in the derivation of this formula?
A density =mass/volume
B potential energy = mgh
C atmospheric pressure decreases with height
D density increases with depth
 
yan_plusheartz said:

Homework Statement



Hey, I have problems solving this question. May I know how to solve this question. Somehow, the answer I got is to the power of negative. can someone show me the step by step solution to this question? (Question 18 from this paper) the link is below.
http://maxpapers.com/wp-content/uploads/2012/11/9702_s13_qp_13.pdf


Homework Equations


E = Fl / Ae


The Attempt at a Solution

I think you are thinking of question 19, correct?

How do the weights of the masses compare to their full size counterparts?
How does the cross sectional area of the cable compare to its full size counterpart?
How do the lengths of the cables compare to their full size counterparts?
 
Oops my mistake, it's question 19 actually.

It is stated that linear dimension of the model is 1/10 of the full size

So e is directly proportional to Fl/A since E is the same for both
Hence e model = (1/10)F x (1/ 10) l / (1/10) A
e full size = F l /A
e model : e full = 10^-1
However, the right answer is 10^2
May I know what is the proper approach to this? Thx
 
yan_plusheartz said:
Oops my mistake, it's question 19 actually.

It is stated that linear dimension of the model is 1/10 of the full size

So e is directly proportional to Fl/A since E is the same for both
Hence e model = (1/10)F x (1/ 10) l / (1/10) A
e full size = F l /A
e model : e full = 10^-1
However, the right answer is 10^2
May I know what is the proper approach to this? Thx
The force is equal to the weight of the mass. The weight of the mass is proportional to its volume. Volume is proportional to its linear dimension cubed cubed. The area of the cable is proportional to its linear dimension squared. The length of the cable is proportional to its linear dimension to the first power.
 
ImageUploadedByPhysics Forums1392296383.288636.jpg


Okay, now that you have explained this to me , I kinda have a rough idea about the question. So here's my working:) is it correct?
However, I can't really relate the last proportionality you explained just now to me . In my working, I just times 1/10 to the force (load) , length and also volume. Is it the right way?
 
yan_plusheartz said:
View attachment 66581

Okay, now that you have explained this to me , I kinda have a rough idea about the question. So here's my working:) is it correct?
However, I can't really relate the last proportionality you explained just now to me . In my working, I just times 1/10 to the force (load) , length and also volume. Is it the right way?
No. 1/1000 the force, 1/100 the area, and 1/10 the length.
 
Okay. Here's my new working. Is it correct ?
ImageUploadedByPhysics Forums1392300235.893834.jpg
 

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