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Math Help - please check DE problem

  1. #1
    Junior Member
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    please check DE problem

    hi everybody, again i'm asking your's help as i have solved some DE problems, it seems to me that i've done all correct but as always my results don't match with those are given i the book.

    1. water flows with the speed of 1,8 liters/sec in the box which has a form of parallelepiped with size 0,6 x 0,75 meters and height 0,8 meters. there is a hole in the bottom of the box with area 2,6 cm^2. calculate the time after which the box will be full.

    2. a funnel has a form of cone with radius R=0,06 meters and height H=0,1 meters. it is set as its top looks down. calculate time in which all water will flow out of it, if it has a hole with diameter of 0,5 cm.

    first one is weird but second one has answer of 28 seconds. i used g=10
    Attached Thumbnails Attached Thumbnails please check DE problem-img_1331.jpg  
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  2. #2
    Senior Member
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    In the first problem, I am worried you may have rounded too imprecisely, especially in the second line. Also, you want the time taken for the height to go from 0 to 0.8, so you can use a definite integral.

    In the second problem, your description has a cone of radius 0.06m while the diagram has diameter 0.06m. Also, I'm not sure where the factor of 0.6 came from in the speed of water leaving the hole.
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  3. #3
    Junior Member
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    yes my bad, there is a mistake in the description, cone has dimeter 0,06m. and there is a formula written in book, telling that speed of water leaving the hole is as written with factor of 0,6
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