Change in Temperature Equation HELP

[FFX]

Hey Everyone,

First time posting here, but you'll probably see me around quite a bit!
If this is in the wrong math spot please let me know, I don't understand the different types of maths.

I have an equation on the change of temperature, I substituted all the values in correctly and thought I was working it out correctly, but my answer came out far too low for me to think I did it correctly. If someone could have a look and give me guidance, that'd be great. The first picture is the full question, the second is me 'trying' to work it out! :(

 

[dalcde]

You should post this in the Homework and Coursework Questions subforum (read the forum rules).

 

[Simon Bridge]

"Put this into MS Excel"
... evil! I take it this is a course on how to use Excel?

Anyway - need to know how you went about it and how you know it came out too low.
That formula is utterly shocking - we'd normally simplify it.

looks like you didn't enter values correctly - I can see from 2nd to last line to last line you've misplaced a zero for example. But it is hard to tell.

You should use separate cells for your input data, then use the cell names as variables in your formula.

 

[FFX]

You should post this in the Homework and Coursework Questions subforum (read the forum rules).

Oh I didn't notice that sticky, I'll post it in the homework area.

"Put this into MS Excel"
... evil! I take it this is a course on how to use Excel?

Anyway - need to know how you went about it and how you know it came out too low.
That formula is utterly shocking - we'd normally simplify it.

looks like you didn't enter values correctly - I can see from 2nd to last line to last line you've misplaced a zero for example. But it is hard to tell.

You should use separate cells for your input data, then use the cell names as variables in your formula.

It's not a course on how to use excel, the first part (part A) is supposed to be done just manually. The second part is supposed to be done on excel I presume. I don't even know how to use excel. I'm doing this math unit externally so it makes it a lot harder as I don't have a teacher telling me how to do anything.

I can't see the misplaced 0, could you be more specific on where it is please? Sorry.

I was just working it out following the basic BODMAS thing, brackets first etc.

I don't have the final answer there because already you can see it's going to come out to a very small number. I presume the question would be absolutely retarded if the temperature was only like 0.0000001 of a change lol.

 

[dalcde]

Q/rcN=$\frac{Q}{rcN}$ or Q/rcN=$\frac{Q}{r}cN$?

 

[Simon Bridge]

OK: so where it says "use program xyz" just use the program you have.
You could use OpenOffice-calc instead or any spreadsheet ... or matlab, or octave.

It's all multiplication and division so BODMAS may not get you into to much trouble ... bear in mind that a common error is to put 5-3+2=0 since it says to do the addition first. We can get rid of BEDMAS by being more careful how we write relations so 5-3+2 = (+5)+(-3)+(+2) and instead of divided-by signs we write fractions and so on.

Conventionally a/bc would be the same as a/(bc) ... the equation writer has been careful with 1/(2(Qs/Q)) and (r/c)f after all. (OTOH: has not been careful with variables - there is a r in the equation and an R in the text... guessing r=R?)

The missing zero, I think, is in the second term in the last line.

octave:174> 440.022/(23.43/0.00000002556)
ans =  4.8002e-07

... you have 4.8002e-06

I think you can expect a very small change in temperature from those figures and that equation - you have to do your reality-check against the physics: what is the situation that leads you to expect a larger temperature change?

If I put k=8.3e-06, and write Qs as Q_s (for clarity) then that equation can be rewritten:$$\Delta T = \frac{kr^2Nf}{Q(1-\frac{Q}{2Q_s})}=\frac{2Q_skr^2Nf}{Q(2Q_s-Q)}$$... (check my algebra) you may find that easier to handle.
Note: the dimensions don't pan out - so either some units are missing ([k]=m^-2 perhaps?) or the equation is wrong.

 

[FFX]

Thank you Simon!
I really appreciate the help! :)