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Wrong Answer, Units issue

BB_14100646
3-Newcomer

Wrong Answer, Units issue

This file is in MathCAD 9, but I'm experiencing the same issue in MathCAD 10. I believe MathCAD is misrepresenting the units. See attached. "Hmp" and "TH" have the wrong values when comparing with example 11.2 at the bottom. I rewrote them as H and T next to them. I substituted "m" and "Ump" for the actual values of 100000 and 1035 and the answers came out correct. So, something is wrong with how "m" and "Ump" are represented.

ACCEPTED SOLUTION

Accepted Solutions
Werner_E
25-Diamond I
(To:BB_14100646)

I attached a Prime 9 worksheet which fixes some of the errors you made.

 

First error is about the temperature unit. You type ° and C and so you defined and angle in degree multiplied by unit Coulomb.

You have to use the unit °C from the unit menu.

Werner_E_0-1757191815780.png

Later you calculate the temperature difference and even with correctly defined temperatures you probably would be surprised by the result you get.

Temperatures are internally stored in basic unit Kelvin.

So we have

Werner_E_1-1757191996885.png

But 725 Kelvin converted to degree Celsius is

Werner_E_2-1757192038251.png

Sure not what you expect as temperature difference. That's the reason we also have 'unit' Delta°C (which basically is an alias for Kelvin).

Werner_E_3-1757192121962.png

 

But the wrong definition of the temperatures had nothing to do with the calculation of TH
Here you made an error when defining Ump. You used "g" for grams, but actually "g" is the predefined constant of gravity. You can tell that its a constant and not a unit by the color - its green and not blue. In Prime you have to use "gm" for unit gram.

Feel free to define a unit "g:=gm" somewhere at the top of the sheet if you want use "g" for gram. Actually "g" is the only unit symbol for gram that is recognised by the SI (International System of Units). "gm" is not allowed by SI standards to avoid confusion with gram-metre g*m.

Werner_E_4-1757192565452.png

 

Now at last you used a factor m when you defined TH. Guess it should be omitted to get the desired result:

Werner_E_5-1757192745725.png

 

 

Prime 9 sheet attached

View solution in original post

2 REPLIES 2
Werner_E
25-Diamond I
(To:BB_14100646)

I attached a Prime 9 worksheet which fixes some of the errors you made.

 

First error is about the temperature unit. You type ° and C and so you defined and angle in degree multiplied by unit Coulomb.

You have to use the unit °C from the unit menu.

Werner_E_0-1757191815780.png

Later you calculate the temperature difference and even with correctly defined temperatures you probably would be surprised by the result you get.

Temperatures are internally stored in basic unit Kelvin.

So we have

Werner_E_1-1757191996885.png

But 725 Kelvin converted to degree Celsius is

Werner_E_2-1757192038251.png

Sure not what you expect as temperature difference. That's the reason we also have 'unit' Delta°C (which basically is an alias for Kelvin).

Werner_E_3-1757192121962.png

 

But the wrong definition of the temperatures had nothing to do with the calculation of TH
Here you made an error when defining Ump. You used "g" for grams, but actually "g" is the predefined constant of gravity. You can tell that its a constant and not a unit by the color - its green and not blue. In Prime you have to use "gm" for unit gram.

Feel free to define a unit "g:=gm" somewhere at the top of the sheet if you want use "g" for gram. Actually "g" is the only unit symbol for gram that is recognised by the SI (International System of Units). "gm" is not allowed by SI standards to avoid confusion with gram-metre g*m.

Werner_E_4-1757192565452.png

 

Now at last you used a factor m when you defined TH. Guess it should be omitted to get the desired result:

Werner_E_5-1757192745725.png

 

 

Prime 9 sheet attached

Werner_E,

 

Thank you so much for your thorough explanation!!! I applied the correct units you suggested and everything works the way it should!

 

Brent

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