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Explain some Energy Questions Please?

  1. Nov 25, 2012 #1
    I answered the questions(not sure if they are right) but I would like to know the best way to explain these questions on a test/quiz.

    1) Describe the transfer of energy that enables a person to climb stairs.

    I put: The person's body first uses the chemical energy from food/water as potential energy. It is then converted into kinetic energy in the form of the action of climbing stairs.

    2)How is energy expenditure and potential of the person at the top of the stairs related?

    I put: Energy is spent in form of kinetic energy by climbing stairs, equals the gravitational potential energy at the top of the stairs.

    3) What would be the most important physical characteristics required for maximum power.

    Not sure what I would put for this one :O

    Thanks :smile:
     
  2. jcsd
  3. Nov 25, 2012 #2

    haruspex

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    If you climb the stairs slowly, very little of the energy ever shows up as kinetic. The muscular force acts to overcome gravity, and not much more. So most goes straight into gravitational PE. If you wanted to, you could expand a little more by explaining that the chemical energy is translated into electrical energy. Muscles work by electrostatic attraction.
    Power is rate of transfer of energy. What would you need to be able to do the above transfers quickly?
     
  4. Nov 25, 2012 #3
    I forgot to include that the the person is running up the stairs as fast as possible.
     
  5. Nov 25, 2012 #4

    haruspex

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    OK, but still only a small amount of energy goes into kinetic if the stairs go more than a few steps. After the initial acceleration, speed is more-or-less constant, so most of the power is going straight into overcoming gravity.
    For the last part, you didn't answer my question: What characteristics would you need to be able to do these energy transfers quickly?
     
  6. Nov 25, 2012 #5
    You would need long legs, long arms to help balance and propel you forward. That's all I can think of :confused:
     
  7. Nov 26, 2012 #6
    Is that sufficient?
     
  8. Nov 26, 2012 #7

    haruspex

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    (Strange - I thought I posted this answer already.)
    To maintain a high throughput you'll need to be able to convert the chemical energy to electrical energy fast (requiring ?), then convert that electrical energy into large forces (requiring?). Hint: these are all things you acquire more of by getting fit.
     
  9. Nov 26, 2012 #8
    Im sorry, but do you mean mechanical energy? To convert the chemical energy you would need a high metabolism? You would need strong muscles to convert that convert the energy into large forces?
     
  10. Nov 26, 2012 #9

    haruspex

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    No, I mean electrical.
    Your metabolism oxidises glucose to obtain the energy to form ATP. This is the body's form of energy-to-go. To sustain doing this rapidly (as opposed to short bursts of activity) requires a high throughput of of oxygen and glucose. So that's lungs, heart and the blood capillaries that deliver to the muscles.
    The ATP drives electron transport, setting up electrostatic potentials along layers of muscle. Electrostatic attraction causes the muscles to contract. To generate a large force you need many layers of muscle working in parallel.
     
  11. Nov 27, 2012 #10
    Oh Thank you!

    I had another quick question if you don't mind :shy:

    Which sports require a person to a) generate a lot of force, b) do much work c) develop great power
    (I used one sport/event)
    a)A weight lifter, doing a dead lift of 105kg would require him/her to generate a lot of force in order to lift the weights

    b) The weight lifter would also have to do a lot of work in order to follow through the motion of a dead lift with the 105kg weights.

    c) The weight lifter would also have to develop great power in order to actually move the weights.

    Are these answers good?
     
  12. Nov 27, 2012 #11

    haruspex

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    It would be better to find different sports, each exemplifying the particular requirement.
    Weightlifting is clearly a good choice for force.
    A long distance runner would surely do more work per event than a weightlifter.
    I'll let you have another go at a power exemplar.
     
  13. Nov 27, 2012 #12
    A lineman in football would need to develop a lot of power, in order to stop a running back from getting past him.

    or

    A quarterback would need to develop great power in order for him to throw the ball great distances.
     
  14. Nov 27, 2012 #13

    haruspex

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    Not a sport I know anything about, but it sounds reasonable. I was thinking of a sprinter, which I'm guessing is what a lineman needs to be.
     
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