document.write( "Question 1186725: An electric kettle contains 1.5 litres of water at 20°C. Find;
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\n" ); document.write( "c) If the element is rated 1 000 W, how long does it take the water to come to the boil? [Ans.: 8 min 24s.]\r
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Algebra.Com's Answer #817885 by math_helper(2461)\"\" \"About 
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document.write( "It takes 4200J to raise 1kg of water by 1°C\r
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document.write( "a) To boil, you must raise the temperature to 100°C  (1 atmosphere of pressure assumed).   That's a change of 100-20 = 80°C\r
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document.write( "1.5l has a mass of 1500g or 1.5kg\r
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document.write( "80*1.5*4200 = 504000J\r
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document.write( "Same calculation including unit analysis:
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document.write( "80°C*1.5kg*4200J/kg/°C = 504000J\r
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document.write( "b) It takes  2260J/g of heat to turn water at 100°C into steam.
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document.write( "One half of the water in this case is 0.5*1.5kg = 0.75kg\r
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document.write( "2260J/g = 2260000J/kg * 0.75kg = 1695000J\r
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document.write( "c) One watt is one joule per second  (1W = 1J/s)  Watts are units for POWER (work per unit time) while Joules are units of ENERGY or WORK.\r
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document.write( "1000W ==>  1000J/s * t  work can be done in t seconds\r
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document.write( "504000J = 1000J/s * t ==>  t = 504sec ( =  8min 24sec )
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