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MC_BT_181-Visitor
1-Visitor
October 14, 2018
Solved

how to solve for variable with units

Hi guys!

I'm new here, trying to learn the basics of mathcad prime 4. I'm having trouble solving what I thought was a simple operation.

 

I'm trying to get a numerical value for k, but I can't make it work. I tried looking in the help and googling, but I'm not getting any closer. I know the answer is probably simple, but I'm just not finding it. So I was hoping for some advice and help on how to write this stuff in mathcad so it understands what I want to do..

 

One last thing, k is a factor in wind resistance (Wind resistance = k * velocity)

 

EDIT: I tried removing all units, which seems to work. But then I have to reassign all my units again, which is rather annoying.. I believe there is a way, which I'm just not seeing (yet)

MC_BT_18Answer
1-Visitor
October 15, 2018

Updated worksheet, with the solution 🙂

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4 replies

RichardJ19-Tanzanite
19-Tanzanite
October 15, 2018

The symbolic solver does not understand units, so the numeric solve block is the best option. You need to multiply the guess value of k by units of kg/s. This should be obvious, because the units in the exponential must cancel.

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MC_BT_181-VisitorAuthor
1-Visitor
October 15, 2018

Well, I tried assigning my guess value for k a unit of kg/s, but it still won't work. I end up with the error that the units aren't compatible..

 

EDIT: Just got help from support. Now it works, by making the function v(t) to v(t,k) instead

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RichardJ19-Tanzanite
19-Tanzanite
October 15, 2018

Sorry. I noticed v(t,k) problem, but forgot to mention it.

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MC_BT_181-VisitorAuthorAnswer
1-Visitor
October 15, 2018

Updated worksheet, with the solution 🙂

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