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Thermal Physics

Scorching goIITian

Joined:	1 Feb 2007
Post:	297

5 May 2007 12:34:37 IST

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472

heat and thermodynamics.....

None

a chef fills tap water at 15 deg centi in a thermos flask and shakes it 30 times per min. if the water falls by a height of 30 cm inside the flask in each shake, the time required to boil the water in this way is approximately?

A)3970 min

B)4389 min

C)5600 min

D)7890 min

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Comments (4)

SYED UZAIR MEHDI

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Joined: 23 Apr 2007

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5 May 2007 12:55:43 IST

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U dud not mention the amount of water that should be boiled.

Bhupesh Mohanty

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Joined: 29 Dec 2006

Posts: 1037

5 May 2007 18:22:53 IST

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Dear
You need to find the net gain in its Energy( It can be found out as if the water is falling from height thus getting it KE converted from initially stored PE as it falls some height every second you mentioned in your question )then use Houls equivalent of heat to equate it to net get in thermal energy i.e ms

+ ml = 4.2 ( PE )

mass will be canceled eventually

Venkatesh Ganesh

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1 Sep 2009 16:26:01 IST

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The answer to this question is pretty simple..

But again, there is some data missing.. Like the initial height level of the water in the flask..

dV = (V)(k)(dT) where V is the initial volume of water in the flask.. dV=change in volume and dT=change in temperature.. k is the coefficient of cubical expansion of water...

As V = (A)(H)(D) where A , the area of cross section of the flask and D the density of the water are constants, H is height level of water

dV = (V)(k)(dT) ------> (A)(D)(dH) = (A)(D)(H)(k)(dT)

dH = H*k*dT... according to the question, dH/dt= -900cms/min ....and at this point we need the initial height which is missing...

Venkatesh Ganesh

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Joined: 13 Aug 2009

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1 Sep 2009 16:30:03 IST

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and Mr Bhupesh, why are taking into account mL? the water just has to boil right? it does not have to get converted to steam..

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