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Thread: rate problem with separation of variables

  1. #1
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    Exclamation rate problem with separation of variables

    The rate at which a substance dissolves in a solution is proportional to the amount of the substance that is present. Thirty grams of sodium chloride are put in a litre of water , and is found that 1 hr later only 10g are left. How much will be left after 30min?

    i have no idea how to do this!
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  2. #2
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    Quote Originally Posted by shawli View Post
    The rate at which a substance dissolves in a solution is proportional to the amount of the substance that is present. Thirty grams of sodium chloride are put in a litre of water , and is found that 1 hr later only 10g are left. How much will be left after 30min?

    i have no idea how to do this!
    The rate of change of the substance is porportional to the amount of the substance. The instantanous rate of change in the derivitive. $\displaystyle N'=\alphaN$Use this to work out what the feunction for N is. Then input your numbers.
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  3. #3
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    Quote Originally Posted by shawli View Post
    The rate at which a substance dissolves in a solution is proportional to the amount of the substance that is present. Thirty grams of sodium chloride are put in a litre of water , and is found that 1 hr later only 10g are left. How much will be left after 30min?

    i have no idea how to do this!
    The rate of change of the substance is proportional to the amount of the substance. The instantaneous rate of change in the derivative. $\displaystyle N' =\alpha N$Use this to work out what the function for N is. Then input your numbers.
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