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lilai3

  • one year ago

WILL REWARD MEDAL/ FAN!!((((: The fuel value of peanuts is 25 kj/ gram. If an average adult needs 2800 kilocalories of energy a day, what mass of peanuts would meet an average adult's energy needs for the day? Assume all of the fuel value of the peanuts can be converted to useful energy.

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  1. UnkleRhaukus
    • one year ago
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    1 adult's energy requirement = 2800 kc/day how many kilo calories are required "for the day"?

  2. lilai3
    • one year ago
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    2800?

  3. UnkleRhaukus
    • one year ago
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    yes,

  4. UnkleRhaukus
    • one year ago
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    how many joules of energy, is 1 kilocalorie?

  5. lilai3
    • one year ago
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    4.184

  6. UnkleRhaukus
    • one year ago
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    so how many joule of energy is 2800 kilocalories, i.e. 2800 [kc] x 4.184 [j/kc] =

  7. lilai3
    • one year ago
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    11715.2 joules?

  8. UnkleRhaukus
    • one year ago
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    So , we have a requirement of 11715.2 [ j ] . And, we know the fuel value of peanuts is 25 [ kj / g ]

  9. lilai3
    • one year ago
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    yeah

  10. UnkleRhaukus
    • one year ago
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    wait a minute 4.184 kilojoules* of energy, is 1 kilocalorie!

  11. UnkleRhaukus
    • one year ago
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    so we have 11715.2 [kj ] .

  12. lilai3
    • one year ago
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    yeah. how do you set it up?

  13. UnkleRhaukus
    • one year ago
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    food value [ kj/g ] = energy [ kj ] / mass [ g ] so mass [ g ] = energy [ kj ] / food value [ kj/g ]

  14. lilai3
    • one year ago
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    mass = 4.184 kj / 25?

  15. lilai3
    • one year ago
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    oh and then you just divide it and the answer will be in grams?

  16. UnkleRhaukus
    • one year ago
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    yeah , what do you get?

  17. UnkleRhaukus
    • one year ago
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    doe it seem like a reasonable result?

  18. lilai3
    • one year ago
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    0.17 grams

  19. lilai3
    • one year ago
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    is that correct?

  20. UnkleRhaukus
    • one year ago
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    wait, a minute

  21. UnkleRhaukus
    • one year ago
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    mass of peanuts [g] = 11715.2 [kj ] / 25 [kj/g]

  22. UnkleRhaukus
    • one year ago
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    the energy required is the 11715.2 [kj]

  23. lilai3
    • one year ago
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    468.61 grams?

  24. lilai3
    • one year ago
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    that feels more correct than the answer I got less than 1 last time

  25. UnkleRhaukus
    • one year ago
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    yeah, about half a kilo seems reasonable to me

  26. lilai3
    • one year ago
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    so basically we just had to convert kilocalories to kilojoules to get the mass?

  27. UnkleRhaukus
    • one year ago
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    first, we found the energy required in the time considered (one day) then we converted the energy from kilocalories to kilojoules and then from kilojoules, we used the fuel value of peanuts to find the mass of peanuts that provides this energy

  28. lilai3
    • one year ago
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    Oh, okay. I see how it relates to the problem now. Thanks.

  29. lilai3
    • one year ago
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    I have one more if you don't mind.

  30. lilai3
    • one year ago
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    The specific heat of aluminum is 0.902 joule / g x Celsius and that of silver is 0.235 joules / grams x Celsius. You have two spoons of equal masses. One is made of aluminum and other silver. Which spoons would increase in temperature faster in a pot of hot soup? Why?

  31. lilai3
    • one year ago
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    This one is so hard

  32. lilai3
    • one year ago
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    Do you think you can help me with this one?

  33. UnkleRhaukus
    • one year ago
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    if we look at the units of specific heat capacity, that is \([\frac{\textrm j}{\text g\,°\text C}]\)

  34. lilai3
    • one year ago
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    yep

  35. UnkleRhaukus
    • one year ago
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    the units say the specific heat capacity is: the energy [joules] to heat a mass [grams] by a temperature [°C]

  36. lilai3
    • one year ago
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    yeah, i understand that.

  37. UnkleRhaukus
    • one year ago
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    so which spoon takes the lesser amount energy transfer to heat up

  38. lilai3
    • one year ago
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    Would it be the silver? Since 0.235 is less than 0.902 joules? So then it would take less amount for energy to heat?

  39. UnkleRhaukus
    • one year ago
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    yep, from experience, we know that metals are good conductors of heat [ metals feel very cold on a normal day, or burn us quickly if they are hot and we touch them ]

  40. UnkleRhaukus
    • one year ago
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    silver is a 'better' metal than aluminium more shiny and much better conductor

  41. lilai3
    • one year ago
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    so the aluminum will be faster to heat up in a pot of hot soup because 0.902 joules is greater than 0.235 joules.

  42. UnkleRhaukus
    • one year ago
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    nope the Al takes more energy to transfer temperature

  43. UnkleRhaukus
    • one year ago
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    (which takes more time)

  44. lilai3
    • one year ago
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    wait so the higher the joule, the more energy it requires for it to heat something up?

  45. UnkleRhaukus
    • one year ago
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    more to heat it up AND more to cool it down

  46. lilai3
    • one year ago
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    so silver will increase the temperature faster due to it's smaller joule, which makes the process of heating faster than the alumiunum?

  47. UnkleRhaukus
    • one year ago
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    the mass are the same , the comparison is the joule to degree ratio

  48. lilai3
    • one year ago
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    So my answer is going to be The silver spoon will increase in temperature faster than aluminum since silver has a smaller joule. The higher the number of joules, the more energy it requires to heat up something.

  49. lilai3
    • one year ago
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    is it okay? should i add anything?

  50. UnkleRhaukus
    • one year ago
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    The silver spoon will increase in temperature faster than aluminium spoon, since the masses are the same, and silver has a smaller specific heat than aluminium: The greater the specific heat, the more joules of energy must transfer to the spoon; the more time is required for soup to heat the spoon by a given amount.

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