physics questions

[cserra87]

Is it possible for the Opted test to ever be wrong? Or is it just me..

Which of the following is the cost of lighting a 100 W lamp for 10 hours at $.10 per kilowatt hour?
i MADE 100 w = .100kWatts and then multipled 10x.100=$1.00
however the right answer is $.10 ...?

A 12-volt battery with an internal resistance of 1 Ohm. Which is the current in amperes that flows in the circuit?

V= IR so 12=I(1) so I= 12.. but the right answer is 3 .... ?

I may just be shot from all the studying I've been doing but I can't seem to figure out what is wrong with these two problems.. help if you can.. thanks!

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[OD4eyes]

Is it possible for the Opted test to ever be wrong? Or is it just me..

Which of the following is the cost of lighting a 100 W lamp for 10 hours at $.10 per kilowatt hour?
i MADE 100 w = .100kWatts and then multipled 10x.100=$1.00
however the right answer is $.10 ...?


There is 100Watts X 1kilowat/1000 watts = 1/10 of a kilowatt
10 hours X 1/10 = 1 kilowatt... the question reads that it is $.10 per very kilowatt... hence 10 cents...

 

[live2serve]

Hi cserra87,
For the first problem (regarding the cost for the light bulb), the Opted answer is indeed correct. OD4Eyes explained it with the proper math, but his units are not quite right, so it still may be a bit confusing. The last line of his post should actually be working in Kilowatt Hours (KwHrs). Actually, here this may be easier. I've written the problem out in MS Paint (so pardon the sloppiness as it's difficult to write clearly with a mouse). I've tried to write out (and show canceling of) the units in a logical manner. I hope this makes sense.

Does that clear things up for you? In your math, you had converted to Kw properly, and multiplied by 10 hours to give you kilowatt hours, but never completed the COST per KILOWATT HOUR. Get it?

As for the internal resistance problem, I believe that one is a opted error. I think that exact problem has been mentioned here on the forum in the past, if I'm not mistaken!? Your formula, and math are correct.

Actually, I found a thread talking about it. Check out blysssful's response here: http://forums.studentdoctor.net/showthread.php?t=649863

 

[cserra87]

thanks guys i got it now!!!