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  • (January 12, 2023, 01:18:11 AM)

Author Topic: My teaches task (very hard math)  (Read 4336 times)

Greyzern

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My teaches task (very hard math)
« on: August 21, 2009, 10:53:51 AM »
Hello i wonder if some of you are good in math?

so well i got this task for my teacher, and i wonder if any of you can solve it? :p


A watertank got volum at 200 litre with water.

The water is adjusted to 70*C and that water that comes inn to the tank is 10*C. on the watertank there is a sign that says: up to 2000W
with 230 V. the effectdegree is at 0,95.

Now find out the power that it takes from the powernett.

how many kWs you need to warm up the water from 10*C to 70*C

Note the warmcapatity is at 1,16 Wh/(kg * k ) = 4.186 kJ / (kg * K )

how long time with it take to heat up the water?

take what you pay for your power were you live, and find out what you need to pay to warm up the water in the watertank


well hope some of you can find out this :)


sorry for my bad english :D
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Novice

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Re: My teaches task (very hard math)
« Reply #1 on: August 21, 2009, 11:16:07 AM »
Quote from: Chris on October 08, 2008, 07:58:43 PM
Additionally, no matter how stupid another member's question(s) may seem to you, please refrain from mocking them because of their question(s).

 . . Must  . . not . . mock . .
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xolik

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Re: My teaches task (very hard math)
« Reply #2 on: August 21, 2009, 11:27:04 AM »
*has no idea*
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Greyzern

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Re: My teaches task (very hard math)
« Reply #3 on: August 21, 2009, 11:27:24 AM »
Quote from: Novice on August 21, 2009, 11:16:07 AM
. . Must  . . not . . mock . .


:o

comon gimme a awnser :>
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xolik

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Re: My teaches task (very hard math)
« Reply #4 on: August 21, 2009, 11:28:21 AM »
Quote from: Greyzern on August 21, 2009, 11:27:24 AM

:o

comon gimme a awnser :>

If somebody solves this for you, how do we know you won't just vanish from the forum? That would be mean of you to just use us up then toss us aside like a cheap hooker.  :cry:
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Greyzern

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Re: My teaches task (very hard math)
« Reply #5 on: August 21, 2009, 11:32:16 AM »
Quote from: xolik on August 21, 2009, 11:28:21 AM
If somebody solves this for you, how do we know you won't just vanish from the forum? That would be mean of you to just use us up then toss us aside like a cheap hooker.  :cry:

well i just found this forum and its many iteressing threads so ill stay here for a while ;)

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Greyzern

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Re: My teaches task (very hard math)
« Reply #6 on: August 21, 2009, 11:50:10 AM »
well looks like i have to call macguyver for this task...
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macguyver

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Re: My teaches task (very hard math)
« Reply #7 on: August 21, 2009, 12:37:07 PM »
Quote from: Greyzern on August 21, 2009, 11:50:10 AM
well looks like i have to call macguyver for this task...

You keep me out of this.
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Min

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Re: My teaches task (very hard math)
« Reply #8 on: August 21, 2009, 03:19:26 PM »
Hey macguyver.  Good to see you.

This looks like more of a Physics problem than a Math problem to me.
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sociald1077

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Re: My teaches task (very hard math)
« Reply #9 on: August 21, 2009, 10:38:32 PM »
http://www.amazon.com/Physics-Scientists-Engineers-Strategic-MasteringPhysics/dp/0321513339/ref=dp_ob_title_bk

This is my physics book. Should tell you everything you need to know. Outside of that I can't help you cause I honestly forgot most of what I took in my 2 sessions of physics.
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BizB

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Re: My teaches task (very hard math)
« Reply #10 on: August 22, 2009, 08:26:30 AM »
I could help you, but I don't know the metric system.
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pbsaurus

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Re: My teaches task (very hard math)
« Reply #11 on: August 24, 2009, 12:41:34 PM »
I was introduced to it once but it was a total dick.
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TeraHammer

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Re: My teaches task (very hard math)
« Reply #12 on: August 28, 2009, 11:20:22 AM »
Quote from: Greyzern on August 21, 2009, 10:53:51 AM
Hello i wonder if some of you are good in math?

so well i got this task for my teacher, and i wonder if any of you can solve it? :p


A watertank got volum at 200 litre with water.

The water is adjusted to 70*C and that water that comes inn to the tank is 10*C. on the watertank there is a sign that says: up to 2000W
with 230 V. the effectdegree is at 0,95.

Now find out the power that it takes from the powernett.

how many kWs you need to warm up the water from 10*C to 70*C

Note the warmcapatity is at 1,16 Wh/(kg * k ) = 4.186 kJ / (kg * K )

how long time with it take to heat up the water?

take what you pay for your power were you live, and find out what you need to pay to warm up the water in the watertank


well hope some of you can find out this :)


sorry for my bad english :D

Yay for heat capacity



Translation: Warmth in equals mass * Heat capacity * Temperature difference

Assuming 1 kg water = 1 L;

Q = 200 kg * 4.186 * (70-10)    (note, it doesnt matter whether you do this in degrees celcius or kelvin)
here you have Q in kJ.
= about 48 MJ

But unfortunately the machine isnt perfect. With an efficiency of 19/20 you need 20/19 more so thats 50,5 MJ

1 kWh = 3,6 MJ, so 50,5 MJ = 50,5/3,6 = 14 kWh needed

2000W = 2000J/s= 2 kJ/s = 0,002 MJ/s. So for 50,5 MJ needed are 50,5/0,002 = 25000 s, or 7 hours.

For the price you'll have to look yourself how much 1 kWh costs; 14 kWhs are easy to calculate then.
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ivan

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Re: My teaches task (very hard math)
« Reply #13 on: August 28, 2009, 03:46:56 PM »
I was busy working on this when I noticed my rates have gone up. So I recalculated, and was about to post the result, when the rates went up again. In other words, it's a moving target, and very difficult to find an exact solution. But it's around 5000 yen, I think, if the exchange rates hold.
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pbsaurus

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Re: My teaches task (very hard math)
« Reply #14 on: September 04, 2009, 10:46:58 AM »
Don't forget transaction fees.  Often it's better to go with a launderer and go off-grid.
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