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kym02 Group Title

The specific heat capacity of water= 4200 J kg-1K-1 1) How much heat energy is required to warm a) 1 kg of water from 14°C to 15°C; b) 5 kg of water from 14°C to 15°C; and c) 5 kg of water from 14°C to 22°C. THANK YOU!!

  • one year ago
  • one year ago

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  1. kym02 Group Title
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    \[J kg ^{-1} K ^{-1}\] this is the correct way of writing the unit

    • one year ago
  2. AravindG Group Title
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    Use the formul heat required =\(mc \Delta t\)

    • one year ago
  3. chmvijay Group Title
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    q=McDelta T

    • one year ago
  4. AravindG Group Title
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    where m is mass c is specific heat capacity ,delta t=change in temperature

    • one year ago
  5. kym02 Group Title
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    ok thanks

    • one year ago
  6. AravindG Group Title
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    yw :)

    • one year ago
  7. kym02 Group Title
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    i worked it out...is the answer 4200J

    • one year ago
  8. AravindG Group Title
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    a b or c?

    • one year ago
  9. kym02 Group Title
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    for a)

    • one year ago
  10. AravindG Group Title
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    right !

    • one year ago
  11. kym02 Group Title
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    hmm and b) is 21000J while c) is 1.68*10\[1.68\times10^{5}\] am i right???

    • one year ago
  12. AravindG Group Title
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    yep :)

    • one year ago
  13. kym02 Group Title
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    was it that simple?

    • one year ago
  14. kym02 Group Title
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    question 2! one way to measure the energy contained in a beam of x-rays is to absorb the beam by a piece of pure graphite. If x-rays are shone on to a cavity in a block of graphite of mass 10 g (0.01 kg), and a rise in temperature of 0.005K, work out the energy supplied by the beam.

    • one year ago
  15. kym02 Group Title
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    oh and the specific heat capacity of graphite is 600\[J kg ^{-1}K ^{-1}\]

    • one year ago
  16. AravindG Group Title
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    same formula !

    • one year ago
  17. kym02 Group Title
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    ok......just making sure. question 3! An electric drill consuming energy at a rate of 200 W is used to make a small hole in a block of copper of mass 2 kg. Assuming that 80% of the electrical energy used ends up in the block as heat, and that this heat is spread evenly throughout the block, estimate its rise in temperature in 10 seconds.

    • one year ago
  18. austinL Group Title
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    Why dont you make a new question? rather than lump several into one post?

    • one year ago
  19. luckythebest Group Title
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    ok @kym02 i'll give a brief info. so energy is 200 W i.e. it uses 200 J in 1 second, correct?

    • one year ago
  20. kym02 Group Title
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    um i honestly dont know....im a beginner. Dont really know about this stuff! sorry!

    • one year ago
  21. luckythebest Group Title
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    Ok, then there is one concept. W means Watt. Watt is the unit of power of a machine. We say that the power of a machine is the amount of work it can do in 1 second.(i.e. rate of doing work,) Hence its unit is Watt(W) also expressed as Joule/second. so 200 W basically means that the machine will use 200 Joules of energy in 1 second. Ok?

    • one year ago
  22. kym02 Group Title
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    ok i understand.

    • one year ago
  23. luckythebest Group Title
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    Fine. so if the machine uses 200 Joules of energy in 1 second, how much of energy would it use in 10 seconds?

    • one year ago
  24. kym02 Group Title
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    2000 J.

    • one year ago
  25. luckythebest Group Title
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    Ok. 2000 J is the electrical energy used. Now he says that 80% of this 2000 J is used as heat energy. So what is 80% of 2000 ?

    • one year ago
  26. kym02 Group Title
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    1600

    • one year ago
  27. luckythebest Group Title
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    Thats right. So this 1600 is the heat energy. As shown above, Heat energy = Mass x sp. heat capacity x rise in temp. You have mass = 2 kg, sp. heat capacity(c) = 400 JKg^-1K^-1, can you find the rise in temperature?

    • one year ago
  28. kym02 Group Title
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    i dont know that one, do i have to transpose?

    • one year ago
  29. luckythebest Group Title
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    Yep you have to. above there was a formula mentioned Heat energy = m x c x delta T Here Heat energy = 1600, m = 2 kg, c = 400 J/KgK, u need to find delta T

    • one year ago
  30. luckythebest Group Title
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    m means Mass; c means specific heat capacity and delta T means the rise in temperature.

    • one year ago
  31. kym02 Group Title
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    \[E _{H}=mcΔT\] so the temperature rise will be: EH divided by mass times c am i right?

    • one year ago
  32. luckythebest Group Title
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    Thats perfectly correct. Just type d ans also when you find it. :)

    • one year ago
  33. kym02 Group Title
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    ok i will, im working on it

    • one year ago
  34. kym02 Group Title
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    Is the answer 2°C?

    • one year ago
  35. luckythebest Group Title
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    Yes. :)

    • one year ago
  36. kym02 Group Title
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    yes!!!!! thanks :) i have one more question though

    • one year ago
  37. kym02 Group Title
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    a)How much potential energy does a 2.0 kg lump of copper possess when it is lifted 3.0 m from the ground? (Take g to be 10 N kg^-1.) b) If it is dropped, how much kinetic energy will it have just before it hits the ground? c) If all that energy is converted to heat, and if all that heat goes into the copper, what rise in temperature would you expect? That's all ! :)

    • one year ago
  38. luckythebest Group Title
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    a) m = 2, h = 3, g = 10. Use Potential Energy = mgh. b) Potential Energy found in a) = Kinetic Energy (By law of conservation of energy) c) Whatever PE you get, assume that as heat energy, the use C , M of copper to find rise in temp by formula EH = m.c. delta T.

    • one year ago
  39. kym02 Group Title
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    whats the unit for a) ???

    • one year ago
  40. luckythebest Group Title
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    a) Any form of energy, whether potential energy, electric energy, heat energy, is expressed in joules( J ) (Please please note this fact; )

    • one year ago
  41. kym02 Group Title
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    ok ok so a) =60 J

    • one year ago
  42. luckythebest Group Title
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    Thats correct.

    • one year ago
  43. kym02 Group Title
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    and c) = \[7.5\times 10^{-2} \deg C\]

    • one year ago
  44. luckythebest Group Title
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    Which is correct, :)

    • one year ago
  45. luckythebest Group Title
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    I hope you're familiar with law of conservation of energy right?

    • one year ago
  46. kym02 Group Title
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    no but i will just look back in a textbook! thank you soooo much!!! you saved me!! :)

    • one year ago
  47. luckythebest Group Title
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    yeah no probs as long as you're familiar with concepts and numericals :)

    • one year ago
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