Calculating Heat Transfer in Copper & Ice Layers

[ilovephysics]

1) a copper bottomed saucepan containing 0.8L of boilling water boils dry in 10min. assuming all the heat flows through the flat coper bottom, which has a diameter of 15cm and a thickness of 3.0mm calculate the temperature of the outside of the copper bottom while some water is still in the pan

i know the variables but i don't know what to do with them...

2) a small pond has a layer of ice 1cm thick floating on its surface. a)if the air temperature is -10 celsius find the rate in cm per hour at which ice is added to the layer. density of ice is 0.917 g/cm3 and its thermal conductivity is 0.592W/mK b) how long does it take for a 20cm layer to build up?

no idea where to start with this one

 

[ilovephysics]

can anyone help me??

 

[quantumdude]

Please read the notice at the top of this Forum entitled https://www.physicsforums.com/showthread.php?t=4825. We normally require that students show how they started and where they got stuck before we offer assistance. Due to the huge volume of homework questions that we get, we tend to jump right to the ones that stick to the posting rules.

So, what have you got so far?

 

[ilovephysics]

ok i kno the formula H=kA(Thot-Tcold)/d
for the first question i kno the k, A (which is area of a circle), i kno d, which is 0.003m, I am not sure about the Thot and T cold though i don't really understand those, i think Thot is 100 degrees because it is boiling? I am pretty much get stuck there with the variables

the second question i really don't know where to start, i think its using the same formula again but i don't know where density comes into play, and sorry about the rules thing I am taking a look at it

 

[ice87]

First off, you must be in phys153 in UBC, because I got the exact same problems. For 1, you first find out the energy it took to boil all the water, and that's Lf*m. You then find find the power by dividing the energy you just found by the time. Since H measures the heat transfer for joules/second, you can just replace H with the power value, and the rest is just easy.

I don't get number 2 either, I tried to find out in my tutorial class, but i got no help from the TA.

 

[ilovephysics]

lol yeah i am in 153 UBC, thanks a lot for the help on the first question...yeah the last question i have no idea where to start i have my tutorial soon so hopefully they can help me with that one

 

[ice87]

well supposedly you're suppose to use some integral crap, but i dun know how to do it.