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MC_BT_181-Visitor
1-Visitor
October 14, 2018
Solved

how to solve for variable with units

  • October 14, 2018
  • 2 replies
  • 4595 views

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)

Best answer by MC_BT_18

Updated worksheet, with the solution 🙂

2 replies

R
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.

M
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

R
RichardJ19-Tanzanite
19-Tanzanite
October 15, 2018

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

M
MC_BT_181-VisitorAuthorAnswer
1-Visitor
October 15, 2018

Updated worksheet, with the solution 🙂

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