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Need help

  1. Sep 15, 2010 #1
    need help with these questions

    How many tons of coal would be needded each year to provide enery needs for the averaage person in USA.
    Assume us population =300million, coal% =23

    b. A windmill produces 1400watts of electric power that is used to heat water. The efficiency is 100%. How long will it take to raise the temperature of 40gallons of water by 50F

    c. A 5kg mass is attached to the end of the string 2 meters long. The other end is fixed to a hook to make a simple pendulum. Initially, the mass is held so that the string is horizontal, the mass is then released. At the point when the string is vertical, what is the kinetic energy of the mass

  2. jcsd
  3. Sep 15, 2010 #2


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    You have to show what you've tried to do to solve the problems
  4. Sep 15, 2010 #3
    C. KE= 1/2mv2

    5KG = MASS
    V= ? D/S
    so since velocity is not given , how do I go about that.
  5. Sep 15, 2010 #4
    I really do not know a and b and thats why am looking for help.
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