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Homework Help: Things are heat'n Up!

  1. Dec 3, 2004 #1
    Hello again Everyone. I am on to conduction, convection, radiation and the stoppage of all molecular motion. Very complicated information for me. I have completed my next on-line module and about to take my self-assessment quiz. Please review my answers (marked with an asterisk) and let me know what you think. Remember, I will provide commentary when asked so let me know which ones are correct. For those that are wrong you can provide some guidance. Not necessarily the correct answer. Thanks and Holidays to everyone.

    1. How many calories are required to heat 600 g of water from 23° C to 33° C?
    a. 60
    b. 600
    c. 6000*
    d. 13800

    2. What effect would there be on Joule's experiment if the mass fell rapidly, hit the floor with substantial speed, and this was ignored?
    a. Nothing. The loss in gravitational potential energy would still be the same.
    b. Nothing. The kinetic energy is converted to heat when the mass hits the floor.*
    c. The number of joules equivalent to 1 calorie would be larger.
    d. The number of joules equivalent to 1 calorie would be smaller.

    3. A typical jogger burns up food energy at the rate of about 40 kJ per minute. How long would it take to run off a piece of cake if it contains 400 Calories (about 1,700 kJ)?
    a. 1 min.
    b. 4.25 min.*
    c. 10 min.
    d. 42.5 min.

    4. Which of the following statements does NOT correctly describe what happens when a hot block is placed in contact with a cool block?
    a. Heat flows from the hot block to the cool block.
    b. The average kinetic energy of the particles decreases in the hot block and increases in the cool block.
    c. The temperature of the hot block decreases and that of the cool block increases.
    d. Temperature flows from the hot block to the cool block.*

    5. The first law of thermodynamics is a re-statement of the law of conservation of:
    a. Angular momentum
    b. Linerar momentum
    c. Mechanical energy
    d. Energy*

    6. The third law of thermodynamics:
    a. Is a restatement of the law of conservation of energy*
    b. Says that heat cannot be completely converted to mechanical energy
    c. Says that we can never reach the absolute zero temperature.
    d. Says that all motion ceases at absolute zero.

    7. The boiling point of liquid nitrogen at atmospheric pressure is 77 K. Which of the following temperatures is the closest to the temperature of an open container of liquid nitrogen?
    a. 76 K
    b. 77 K*
    c. 78 K
    d. 293 K

    8. Which of the following is NOT a method of transporting thermal energy from one place to another?
    a. Radiation
    b. Condensation*
    c. Conduction
    d. Convection

    9. In conduction, thermal energy is transported by:
    a. The movement of a fluid.
    b. The collision of particles.*
    c. Electromagnetic fields.
    d. The propagation of sound waves.

    10. In radiation, thermal energy is transported by:
    a. The movement of a fluid
    b. the collision of particles.
    c. Electromagnetic fields.*
    d. The propagation of sound waves.
  2. jcsd
  3. Dec 3, 2004 #2

    Andrew Mason

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    It looks to me like you should review questions 2, 3 and 6.

  4. Dec 6, 2004 #3
    Thanks AM. No hints but I will try again. I re-read the module and then looked at the questions again.

    (2) I am totally confused and not even sure exactly what they are looking for.
    (3) Boy am I calorically as well as mathematically challenged. At a rate of 40 kJ per minute then 1,700 kJ would be burnt of in 1700 divided by 40 or (d.) 42.5 minutes - It would be one hell of a jogger to burn 400 calories in 4+ minutes.
    (6) (b) Says that heat cannot be completely converted to mechanical energy
  5. Dec 6, 2004 #4
    Check no. 4!
  6. Dec 6, 2004 #5

    Andrew Mason

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    Joule used a dropping weight to turn a paddle wheel in a volume of water and measured the temperature as a function of loss of gravitational potential of the mass. If some of that gravitational potential energy was converted into kinetic energy of the dropping mass (i.e. was not used to turn the paddle wheel) and this was ignored, the comparison of the drop in height to the temperature of the water would result in a lower ratio of [itex]\Delta T/\Delta E[/itex]. So what is the answer?
    I don't think so. Reread the third law. It has to do with reaching absolute zero. 6d) is close but, in fact, an element at absolute zero has positive energy. 6c) appears to be the correct answer.

  7. Dec 6, 2004 #6
    are u sure?....question says does NOT
  8. Dec 6, 2004 #7
    Oooooops! I overlooked that "NOT"...:)
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