- #1

Janinever

- 13

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Hi guys!

I think I need to explain myself before I ask for the advice :) I'm 27 (so been in grade 12 ages ago) - I didn't have science, I wrote it years later. Now I'm enrolled for a Bsc degree in the hope of getting into medical school (very tough in South Africa). I'm putting a lot of time into studying and started physics now - but I'm clueless - so have to start from the bottom and hit a bit of a roadblock!

I got a multiple concept problem - I managed to follow along in the book to where they reached the section just before the answer... but how they get from the final part of the equation to the answer is a mystery - and I see many more like these in the book but no explanation so I'm guessing this part was sort of "assumed knowledge from school".

The problem involves steam beams with concrete on the sides. So with the increase in temp the beams have no space to expand but the concrete is exerting pressure to avoid expansion of the beams. They want to know what pressure the concrete is exerting.

So in the book they mention and explain Youngs Modulus

After some equations have been substituted into others (this i understand which is why I haven't included this) you end up with

Stress = Y (alpha) (T-T0)

and we also know that

y=2.0 x 10^11 N/m^2 and (alpha) = 12 x 10^-6 (Celsius degrees)^-1

Now if you put that into the above stress equation you get :

(2.0 x 10^11 N/m^2) {12 x 10^-6(Celsuis degrees)^-1}(42-23)And now I have no clue further...

the books answer is 4.6 x 10^7 N/m^2

I have no idea how they even get close to this answer. If anyone can help me please explain as if I am a little kiddie :) Doing this after SO many years is really difficult but with many hours of studying I'm really motivated to learn!

Thank you!

I think I need to explain myself before I ask for the advice :) I'm 27 (so been in grade 12 ages ago) - I didn't have science, I wrote it years later. Now I'm enrolled for a Bsc degree in the hope of getting into medical school (very tough in South Africa). I'm putting a lot of time into studying and started physics now - but I'm clueless - so have to start from the bottom and hit a bit of a roadblock!

I got a multiple concept problem - I managed to follow along in the book to where they reached the section just before the answer... but how they get from the final part of the equation to the answer is a mystery - and I see many more like these in the book but no explanation so I'm guessing this part was sort of "assumed knowledge from school".

## Homework Statement

The problem involves steam beams with concrete on the sides. So with the increase in temp the beams have no space to expand but the concrete is exerting pressure to avoid expansion of the beams. They want to know what pressure the concrete is exerting.

## Homework Equations

## The Attempt at a Solution

So in the book they mention and explain Youngs Modulus

After some equations have been substituted into others (this i understand which is why I haven't included this) you end up with

Stress = Y (alpha) (T-T0)

and we also know that

y=2.0 x 10^11 N/m^2 and (alpha) = 12 x 10^-6 (Celsius degrees)^-1

Now if you put that into the above stress equation you get :

(2.0 x 10^11 N/m^2) {12 x 10^-6(Celsuis degrees)^-1}(42-23)And now I have no clue further...

the books answer is 4.6 x 10^7 N/m^2

I have no idea how they even get close to this answer. If anyone can help me please explain as if I am a little kiddie :) Doing this after SO many years is really difficult but with many hours of studying I'm really motivated to learn!

Thank you!

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