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No clue about this problem (Saving the Earth.)

  1. Apr 24, 2008 #1
    Global warming problem (Saving the Earth.)

    This is the problem:
    The Earth's oceans have risen by 20 centimeters over the last 50 years. Suppose that global warming and the rise of the Earth's oceans becomes inevitable, and our only option is to find ways to lower the sea level. One option would be to dig sand from underneath the ocean and place it on dry land. This process requires energy because the sand is being raised to a higher gravitational potential energy. Estimate how much energy would be required to lower the sea level by 1 cm. Assume that the sand is raised by a height of 10 meters, that the density of sand is 2000 kilograms per cubic meter, and that the whole process uses energy at 20 percent efficiency. How does this amount of energy compare to the total energy used by civilization in one year? How much new land would be created? Note: Approximate freely as needed.

    I have no clue to where i should even start. ive been sittin, starring, trying to figure it out, but the way the prof doesnt give us any notes or anything - i doubt that i can get anywhere with this. any help is appreciatedd
    Last edited: Apr 24, 2008
  2. jcsd
  3. Apr 24, 2008 #2


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    Homework Helper

    The oceans cover about 70% of the surface of the Earth, so you need to find the surface area of a sphere the size of Earth and take 0.7 of that. If you multiply that area by a thickness of 1 cm. = 0.01 m, you will have an estimate of the volume of sand that would need to be moved.

    You are given a density for sand, so you can find the mass of sand that has to be moved.

    The energy required to move all this mass is taken to be the work required to lift its weight by a distance of 10 meters (I've no idea why this number is chosen -- the average ocean depth is 1 kilometer!). Since the process does this work at 20% efficiency, that means 5 times as much energy is consumed from the fuel source than is used to actually do this work.

    I don't know what the intent of the question about the "new land created" is. It seems to me that if you're dumping this sand on dry land, you aren't adding any new surface area above the water level.

    You will find that, for the amount of energy required to do this, this proposal is a pretty dumb idea...
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