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Another math question...

Posers and Puzzles

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It's been a while since I've done differential equations...

v'(t) - k [v(t)]^2 = g

Solve for v(t).

I'd know what to do if the v weren't squared, but I have no idea what to do here.

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Originally posted by Jirakon
It's been a while since I've done differential equations...

v'(t) - k [v(t)]^2 = g

Solve for v(t).

I'd know what to do if the v weren't squared, but I have no idea what to do here.
Had to look at this one for a while, but I finally got something simple:

v'(t) = k[v(t)]^2 + g = (SQRT(k)*v + i*SQRT(g)) * (SQRT(k)*v - i*SQRT(g))

Putting this into a more useable form, we have:

dv / ((SQRT(k)*v + i*SQRT(g)) * (SQRT(k)*v - i*SQRT(g))) = dt

Now just separate the fractions and integrate each one. I have to split, but the answer should follow simply from here. (If no one finishes it, I'll do it when I get home.)

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That's fine. I just used partial fractions from there. Thanks.

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Originally posted by Jirakon
It's been a while since I've done differential equations...

v'(t) - k [v(t)]^2 = g

Solve for v(t).

I'd know what to do if the v weren't squared, but I have no idea what to do here.
I dropped the v dependence in t in intermediary calculations for the sake of a lighter notation.

http://i35.tinypic.com/5bv0h5.gif

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Originally posted by adam warlock
I dropped the v dependence in t in intermediary calculations for the sake of a lighter notation.

http://i35.tinypic.com/5bv0h5.gif
I forgot to add the constant of integration so the last two steps should be -1/v=kt+C which implies v(t)=-1/(kt+C) where C depends on the initial conditions

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Originally posted by adam warlock
I dropped the v dependence in t in intermediary calculations for the sake of a lighter notation.

http://i35.tinypic.com/5bv0h5.gif
Is that your LaTeX typesetting default? It looks strangely ugly. 😕

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Originally posted by Palynka
Is that your LaTeX typesetting default? It looks strangely ugly. 😕
Shamed as I am of admitting it, but it isn't LateX. It was done using MathType and then I exported the solution into a .gif image.

I wasn't at my machine and so couldn't use LateX.

😳 😳 😳

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Originally posted by adam warlock
Shamed as I am of admitting it, but it isn't LateX. It was done using MathType and then I exported the solution into a .gif image.

I wasn't at my machine and so couldn't use LateX.

😳 😳 😳
Enjoy!
http://thornahawk.unitedti.org/equationeditor/equationeditor.php

1 edit
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Originally posted by Palynka
Enjoy!
http://thornahawk.unitedti.org/equationeditor/equationeditor.php
Nice!

http://tinyurl.com/4n4uhn

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