A steam engine has an efficiency of 20%.It is given an energy of 1000 cal.per minute.What is the actual work done by it in joule and in calories?
a) 100 cal,800 J
b) 200 cal,873 J
c)10 cal,80 J
d)100 cal,100 J

- mayankdevnani

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- schrodinger

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- mayankdevnani

@amistre64 @ParthKohli @hartnn @Callsito @Zarkon @Hero @.Sam. @estudier @ganeshie8 @ajprincess @Algebraic!

- mayankdevnani

@Callisto

- amistre64

im not sure since we havent gone over this in my physics class yet, but i would say that 20% efficiency means that 20% of the 1000 cals are used; giving us 200 cals in the answer at least

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## More answers

- anonymous

May I help?

- amistre64

please do :)

- mayankdevnani

ofcourse @SheldonEinstein

- anonymous

;) OK so first of all what @amistre64 discussed in his previous comment is very imp. to do this quest., so @mayankdevnani do you know what does efficiency mean?

- mayankdevnani

ok @amistre64 then

- mayankdevnani

yaa

- mayankdevnani

efficiency=winout/winin*100

- mayankdevnani

right @SheldonEinstein

- anonymous

Yeah or in simpler words it is : \(\large{\frac{\textbf{Output}}{\textbf{Input}}\times 100}\) it is 100%...

- mayankdevnani

yaa

- anonymous

So, what we have is output/input * 100% = 20% , correct?

- mayankdevnani

correct

- anonymous

Ok so now, let me understand the second line of the quest. , is the output = 1000 calorie ?

- mayankdevnani

yaa

- mayankdevnani

then

- mayankdevnani

@SheldonEinstein then

- anonymous

Oh sorry wait!

- mayankdevnani

yaa

- anonymous

I am getting diff. answer so I am checking it, sorry , it will require some patience.

- mayankdevnani

ok

- anonymous

Quest. is wrong

- mayankdevnani

why?? no it is right

- anonymous

Time is not given.. though if you take 1 minute it is 200 cal.

- mayankdevnani

yaa

- anonymous

See , Power = 1000 cal/minute (given)

- anonymous

use this and you will get 200 cal. as answer.

- mayankdevnani

so what's the work done?

- anonymous

W = P * time
if T = 1 second , W = P ...
that's it , find P(output) .. (using efficiency = Ouput/Input *100%) in Cal. per minute , that will be your answer

- anonymous

200 cal.... = WORK DONE

- mayankdevnani

no

- mayankdevnani

but the work done is in joule

- mayankdevnani

@ParthKohli @Preetha

- mayankdevnani

@SheldonEinstein

- mayankdevnani

@myininaya

- anonymous

Is my answer correct, i.e. 200 cal, 873 J ?

- mayankdevnani

yaa

- anonymous

So where is the problem? ?? ? ?

- mayankdevnani

873 J how??

- mayankdevnani

@amriju

- mayankdevnani

@SheldonEinstein how you got it 873J

- anonymous

I got 200 Cal, and it is in options, soo....

- mayankdevnani

but it's wrong

- mayankdevnani

i need solution

- mayankdevnani

can you help me @amriju

- anonymous

200 cal * 4.184 = 836 J (approx. ) not equal to 873 Joule , hence I think the options are wrong..

- mayankdevnani

no it was not wrong

- amriju

work done is 20 percnt of the energy given...thats efficiency....so per minute is 20percnt of 1000 cal...thats 200 cal...convert to joules

- mayankdevnani

so 1cal.=? j @amriju

- amriju

4.2...approx..the correct is 4.187...

- mayankdevnani

is it 4.37

- amriju

nope

- mayankdevnani

why??

- amriju

thats how it is defined...both are units...and 1 cal is defined as 4.187 joules...

- anonymous

That is what I was saying @amriju

- mayankdevnani

in my solution book...the answer is as follows-
\[\frac{20}{100}=\frac{W}{1000}=200 calorie\]
OR
\[200\times4.37=873J\]

- mayankdevnani

is that right?? @amriju and @SheldonEinstein

- anonymous

That is wrong, 1 Cal. = 4.187 Joule NOT 4.37 joule...

- mayankdevnani

ok... thnx... @SheldonEinstein and @amriju

- amriju

u may jst check on wikipedia...and its seems that none of the options are correct...the closest being 200, 837

- amistre64

just for reference
http://www.wolframalpha.com/input/?i=200+calorie+to+joule

- amistre64

if your options are truely: 200,873
then its most likely a typo and prolly meant to be read as 200,837

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