/sci/ - Science & Math » Thread #11100647

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Anonymous Tue 29 Oct 00:39:34 2019 No.11100647 View Reply Original Report

Quoted By: >>11100656 >>11100694 >>11101031 >>11101035 >>11101056 >>11101137 >>11101170 >>11102227 >>11102777

>doing some calc homework online
>assignment is a bunch of problems like pic related
>boomer dad walks in
>what are you working on anyway? Is this """"online learning"""""?
>show him the problem
>Huh, THIS is math?? If I sat down for a few minutes I could probably figure this out...
>last time he did math was algebra 2 in like 1965
>try to explain that it's impossible to solve the problem without a differential equation and that he will never "figure it out"
>he still doesn't get it

Anyone wanna share their /sci boomer stories?

Anonymous

Anonymous Tue 29 Oct 2019 00:43:39 No.11100656 Report

Quoted By: >>11100661

>>11100647
OP is dumb
>muh diffeq

Anonymous

Anonymous Tue 29 Oct 2019 00:45:44 No.11100661 Report

Quoted By:

>>11100656
boom boom brain detected

Anonymous

Anonymous Tue 29 Oct 2019 00:46:20 No.11100663 Report

Quoted By: >>11100680

I took trig in school but want to study calc before I continue my degree. Is there something else I need to learn or do I just start with differentials? Also where can I lookup all the new symbols.

Anonymous

Anonymous Tue 29 Oct 2019 00:52:16 No.11100680 Report

Quoted By:

>>11100663
You're gonna have to brush up on algebra most likely. Just start a khan academy course or something and every time you see them move something around in a way that doesn't make sense to you look up why it's allowed. Also know how the graphs of all the elementary functions look. It helps a lot with understanding limits.

Anonymous

Anonymous Tue 29 Oct 2019 01:01:53 No.11100694 Report

Quoted By: >>11100702 >>11100717

>>11100647
Is this supposed to be calculus?
It does look easy as shit, your dad is probably right
t. electrician tradie

Anonymous

Anonymous Tue 29 Oct 2019 01:06:36 No.11100702 Report

Quoted By:

>>11100694
Solve it without calculus then

Anonymous

Anonymous Tue 29 Oct 2019 01:12:49 No.11100717 Report

Quoted By: >>11100973

>>11100694
At every instant the rate of what's leaving the tank is changing based on how much salt is in the tank. But the amount of salt in the tank is based on the amount that's has entered minus the amount that's exited. It doesn't matter how long you spend on it you're never gonna solve it without calculus.

Anonymous

Anonymous Tue 29 Oct 2019 02:00:32 No.11100861 Report

Quoted By:

ahhh
i remember these online homework calc 1 questions
always with this brine water
probably the only time i saw brine mentioned in my 4 years of college and past 2 years since then

completely forgot how to do this shit btw

Anonymous

Anonymous Tue 29 Oct 2019 02:09:43 No.11100882 Report

Quoted By: >>11100895

The equilibrium state is same amount of salt entering and exiting.
Every min 0.05 * 5 + 0.04*10 kg = 0.65kg enters, so that much must exit.

That means there must be 0.65kg * 1000 / 15 ~= 43.33kg in the tank.

The net inflow of salt is proportional to difference between current concentration and equilibrium concentration. It's like compounding interest but backwards in time.

So we have 43.33 - exp(-k t)

Finally we know that the inflow at t=0 is 0.65kg, so k = 0.65.

Ez pz don't need no stupid dereferential equations.

Anonymous

Anonymous Tue 29 Oct 2019 02:14:53 No.11100891 Report

Quoted By: >>11100927 >>11101020 >>11101062 >>11101085 >>11101098 >>11101182

The equilibrium state is same amount of salt entering and exiting.
Every min 0.05 * 5 + 0.04*10 kg = 0.65kg enters, so that much must exit.

That means there must be 0.65kg * 1000 / 15 ~= 43.33kg in the tank.

The net inflow of salt is proportional to difference between current concentration and equilibrium concentration. It's like compounding interest but backwards in time.

So we have 43.33 - a exp(-b t)

At time t=0 salt is 0, so a = 43.33

43.33 - 43.33 exp(- bt)

At time t=0 inflow of salt is 0.65kg/min so

43.33b = 0.65
b = 0.015

Answer: 43.33 - 43.33 exp(- 0.015t)

Anonymous

Anonymous Tue 29 Oct 2019 02:17:20 No.11100895 Report

Quoted By:

>>11100882
>0.65kg enters, so that much must exit.
wrong. when it enters the pure water it gets diluted.

Anonymous

Anonymous Tue 29 Oct 2019 02:34:01 No.11100927 Report

Quoted By:

>>11100891
wrong

Anonymous

Anonymous Tue 29 Oct 2019 02:54:05 No.11100973 Report

Quoted By: >>11101155

>>11100717
Okay but logically it should be possible to invent calculus to solve it given time. How to do that?

Anonymous

Anonymous Tue 29 Oct 2019 03:10:27 No.11101020 Report

Quoted By: >>11101062 >>11101085 >>11102095 >>11102227 >>11102282

$\frac{dC}{dt} = 0.05*5 + 0.04*10 - C(t)*15$

There you go, its a super basic ODE
>>11100891
Is right that it should be an exponential, but he probably made an algebra error somewhere

Anonymous

Anonymous Tue 29 Oct 2019 03:13:41 No.11101031 Report

Quoted By: >>11101085

>>11100647
This question doesn't seem like it needs differential equations at all. Some basic calculus gives me an answer of 28.1694kg salt after 70 minutes. Does that sound about right?

Anonymous

Anonymous Tue 29 Oct 2019 03:14:29 No.11101035 Report

Quoted By:

>>11100647
my dad actually knows math
Well not as much anymore as he doesn't hasn't needed to do it in decades, but he was the one who taught the basics that kick started my interest in math. Before he started teaching me I was a brainlet, but once he started teaching me I picked it up really quickly and eventually exhausted the entire curriculum for that year and the following year

Anonymous

Anonymous Tue 29 Oct 2019 03:22:21 No.11101056 Report

Quoted By:

>>11100647
You're a faggot for trying to impress your dad with your math problems. Learn some humility.

Anonymous

Anonymous Tue 29 Oct 2019 03:24:13 No.11101062 Report

Quoted By: >>11102095

>>11101020
>>11100891
actually not even an algebra error anon just scooted his t axis forward compared to the problem statement

Anon set t=0 at equilibrium concentration and worked backwards

Problem statement has t=0 at a concentration of 0 and asks you to work forwards

Anonymous

Anonymous Tue 29 Oct 2019 03:33:15 No.11101085 Report

Quoted By: >>11101098 >>11102095

>>11101031
Questions in math rarely, and quite possibly never, have a single answer or "way" to do things. In the field of real analysis there can be 14-15 different proofs for semi-trivial theorems, equivalency theorems linking other theorems, ect. It all depends on the amount of assumptions that you're willing to make, and time you're willing to sacrifice. For instance:>>11100891 makes some genius level jumps in logic, whereas >>11101020's answer fits on one line. I don't really know differential equations though, I've never taken a class on them, nor have I had any exposure to them, so take it with a grain of salt.

Anonymous

Anonymous Tue 29 Oct 2019 03:38:21 No.11101098 Report

Quoted By: >>11101113

>>11101085
>For instance:>>11100891 makes some genius level jumps in logic
He really, really doesn't. That's some pretty elementary modeling he does there.

Anonymous

Anonymous Tue 29 Oct 2019 03:42:14 No.11101113 Report

Quoted By: >>11101122

>>11101098
I don't do modeling

Anonymous

Anonymous Tue 29 Oct 2019 03:43:58 No.11101122 Report

Quoted By: >>11101150

>>11101113
By the sounds of it, you do grade 10 math.

Anonymous

Anonymous Tue 29 Oct 2019 03:48:09 No.11101137 Report

Quoted By:

>>11100647
>Buy a copy of einsteins paper on special relativity
>My dad, a boomer lawyer, takes it from my hands
>"Let me read this before you, im really interested in this"
>Tell him thats fine, that if he needs any help with the math he can call me and ill do my best to explain
>"Dont worry anon, I wont need any help"
>A week later he tells me he got thru the first few chapters with no problem
>Ask him what makes something lorentz invariant
>"Idk, i just skipped over all the boring math bable and read his explanations, im getting a really good grasp at relativity now!"

He quit reading the book a few days later, claimed he had "no time" yet he has read about 3 fiction novels since then. O boy the ego on that man.

Anonymous

Anonymous Tue 29 Oct 2019 03:51:45 No.11101150 Report

Quoted By: >>11101162

>>11101122
Look up the definition of a measure and come back and tell me how that compares to the algebraic jockey work in problems such as these.

Anonymous

Anonymous Tue 29 Oct 2019 03:52:24 No.11101155 Report

Quoted By:

>>11100973
Well sure, given that we already know how calculus works, it might seems "obvious" that, since rate is proportional to amount, you look at some times t1 and t2 and compare between what the rates are then, but then you further realize there are times in bewteen t1 and t2, and accounting for those will refine your answer, and so on and so forth until you reach the conclusions of "infinitesimals", limiting ratios, etc., all good calculus things.
But will the average person who has never learned these things come up with that on their own? I'm not so sure. It seems so obvious to us because we learned it so long ago, when we were (relatively) young, and have since been indoctrinated to qualitatively understand various natural processes via the lenses of calculus and DEs. But there's a reason the average normie struggles to learn this material when their taught it in a specific classroom environment, much less coming up with it themselves.
Honestly, integration might be easier to "derive" because the picture (at least in 1D) is so much more obvious, as evidenced by "Tai's method". Everyone can look at a stop sign and think to themselves, "if I just add more sides, it'll look a lot more like a circle".

Anonymous

Anonymous Tue 29 Oct 2019 03:54:14 No.11101162 Report

Quoted By: >>11101176

>>11101150
>I looked up some analysis on wikipedia, therefore I'm smarter than you.
No one's believing that you understand analysis, but can't do a calculus problem.

Anonymous

Anonymous Tue 29 Oct 2019 03:56:46 No.11101170 Report

Quoted By:

>>11100647
low iq post

Anonymous

Anonymous Tue 29 Oct 2019 03:57:53 No.11101176 Report

Quoted By: >>11101182 >>11101203

>>11101162
I can do the calculus problem, I don't understand why someone would sit there for an hour figuring out how to do it without calculus.

Anonymous

Anonymous Tue 29 Oct 2019 03:59:29 No.11101182 Report

Quoted By: >>11101188

>>11101176
Just shut the fuck up.
>I don't really know differential equations
>For instance:>>11100891 makes some genius level jumps in logic

Anonymous

Anonymous Tue 29 Oct 2019 04:01:15 No.11101188 Report

Quoted By: >>11101192 >>11101202

>>11101182
>differential equations
>calculus
Hmm

Anonymous

Anonymous Tue 29 Oct 2019 04:01:59 No.11101192 Report

Quoted By: >>11101209

>>11101188
how do you know analysis but don’t understand basic differential equations?

Anonymous

Anonymous Tue 29 Oct 2019 04:05:17 No.11101202 Report

Quoted By: >>11102440 >>11102739

>>11101188
Linear ODEs are taught in Calculus classes, you dipshit. They are literally part of calculus. I guess you don't know since you didn't get into AP calc.

Anonymous

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Anonymous Tue 29 Oct 2019 04:05:25 No.11101203 Report

Quoted By:

>>11101176
spoken like a true analyst.
Tell us the answer to pic related.

Anonymous

Anonymous Tue 29 Oct 2019 04:06:49 No.11101209 Report

Quoted By: >>11101219 >>11101223 >>11101229

>>11101192
I never took a class on differential equations, I dunno. I know curl and divergence, green's and stoke's theorem, does that count?

Anonymous

Anonymous Tue 29 Oct 2019 04:09:21 No.11101219 Report

Quoted By: >>11101223

>>11101209
Next time, when you're trying to convince people you're not a retard who just browsed wikipedia, just say you've done vector calculus. No one says what theorems and definitions they've learned like some sperg.

Anonymous

Anonymous Tue 29 Oct 2019 04:10:41 No.11101223 Report

Quoted By: >>11101231

>>11101209
>>11101219
>hurr durr look at me my math dick is as big as yours hurr durr
sorry just some random chem dude

Anonymous

Anonymous Tue 29 Oct 2019 04:11:21 No.11101229 Report

Quoted By:

>>11101209
Nah thats vector calc

An introductory diff eq class should've covered separation of variables, wronskians, laplace transforms, and a bit of linear algebra
At least thats what I remember from it

Anonymous

Anonymous Tue 29 Oct 2019 04:12:14 No.11101231 Report

Quoted By: >>11101245

>>11101223
No one in chem is doing analysis, cocksmoker.

Anonymous

Anonymous Tue 29 Oct 2019 04:14:56 No.11101245 Report

Quoted By: >>11102123

>>11101231
You sound like a very salty engineer, I'm sorry is being a human calculator starting to wear down the braincells in the part of the brain you use for self-control?

Anonymous

Anonymous Tue 29 Oct 2019 12:55:33 No.11102095 Report

Quoted By: >>11102532

"genius leaper" here.
>>11101085
I actually didn't. I knew which form it should from solving diff eqs like this before, and tried to come up with arguments to justify it...
>>11101062
No. Set t=0, and notice how the concentration becomes 0.
>>11101020
This is wrong. You are confusing the amount of salt with the concentration of salt.
If C is the amount of salt, then you need to divide by 1000 to get the concentration, so you should really have
-C(t) * 15/1000

Anonymous

Anonymous Tue 29 Oct 2019 13:15:21 No.11102123 Report

Quoted By:

>>11101245
Not even that anon but your Humanities dropout tier responses are triggering me. Why would you pretend to be smarter than you are on the internet if you're literally too dumb to even fake it? It's really stupid. You can just say that you haven't learned something and that's fine, not everyone knows everything. Only kids want to convince others they know more than they do.

Anonymous

Anonymous Tue 29 Oct 2019 14:07:59 No.11102227 Report

Quoted By: >>11102431 >>11102532

>>11100647
i have a masters degree in physics and never learned how to turn a problem into a diffeq.
i can solve partial diffeq but have no idea how to get to the equation here.
i got as far as
dC/dt=0.65 - ???
>>11101020
can you tell my why -C*15 solves it?

also i dont really get the units, seems like it doesnt work out with this equation

Anonymous

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Anonymous Tue 29 Oct 2019 14:42:44 No.11102282 Report

Quoted By: >>11102431 >>11102532

>>11101020
How does one solve this integral?

Genius Leap Anon

Genius Leap Anon Tue 29 Oct 2019 16:07:30 No.11102431 Report

Quoted By:

>>11102227
> i have a masters degree in physics and never learned how to turn a problem into a diffeq.
It's a really important skill for physicists. Prioritize learning it

>>11102227
Every minute 15 liter leaves the tank. There are 1000 liters. Hence every minute 15/1000 of the tanks water leaves with 15/1000 of the tank's salt.
So it should be -15/1000 C

>>11102282
Look up inhomogeneous linear differential equations.

Anonymous

Anonymous Tue 29 Oct 2019 16:12:27 No.11102440 Report

Quoted By: >>11102441 >>11102734

>>11101202
>AP calc
oh jesus are you annoying. Pull your head from your own ass, saying you got into AP calc is like saying you took intro to biology in highschool at the local CC. Interesting but utterly irrelevant past the first semester of undergrad.

Anonymous

Anonymous Tue 29 Oct 2019 16:14:24 No.11102441 Report

Quoted By:

>>11102440
Actually I take that back, taking a class at a CC shows drive and independent motivation. Taking AP calc just means you were willing to try hard in the bounds of your highschool, the second dumbest part of peoples education after middleschool.

Anonymous

Anonymous Tue 29 Oct 2019 17:07:29 No.11102532 Report

Quoted By:

>>11102227
15 L/min is the rate of fluid flow out of the tank.
We assume the tank is well-mixed for simplicity, so the concentration of the output stream is the samr as the concetration of the tank at any time $C(t)$

>>11102282
Step 1 -> Step 2 is simple separarion of variables
Then all you need to do is a substitution for the expression in the denominator
Recall the anti-derivative of $\frac {1}{x}$ is the natural log.

>>11102095
You're right, left hand side should be $\frac {dm}{dt} = V*\frac {dC}{dt}$ in my defense its been a while and I got sloppy.

Anonymous

Anonymous Tue 29 Oct 2019 18:35:53 No.11102734 Report

Quoted By: >>11102739

>>11102440
>Retard can't understand the obvious implication
Why is this board full of high school retards?

Anonymous

Anonymous Tue 29 Oct 2019 18:38:47 No.11102739 Report

Quoted By: >>11102750 >>11102755

>>11101202
>he thinks ODE’s are taught for more than 2 weeks in a calc class
>>11102734
what you said is stupid though this kind of diff eq is taught in all calc 2 courses and is absolutely trivial

Anonymous

Anonymous Tue 29 Oct 2019 18:41:24 No.11102750 Report

Quoted By:

>>11102739
>this kind of diff eq is taught in all calc 2 courses and is absolutely trivial
That is basically what I said though. How is it stupid?

Anonymous

Anonymous Tue 29 Oct 2019 18:42:27 No.11102755 Report

Quoted By:

>>11102739
Also, I never said that they are taught for more than 2 weeks.

Anonymous

Anonymous Tue 29 Oct 2019 18:49:35 No.11102777 Report

Quoted By:

>>11100647
hes not wrong. its a differential equation problem

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