Finding Water Depth in an Inverted Cone

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Homework Help Overview

The problem involves an inverted right circular cone collecting water at a steady rate, with specific questions regarding the depth of water after a set time and the rate of increase of that depth. The subject area includes geometry and calculus, particularly related to volume and rates of change.

Discussion Character

  • Conceptual clarification, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the relationship between volume and depth, questioning the original poster's interpretation of depth in terms of volume. There are attempts to clarify the distinction between depth and volume, as well as the implications of the units involved.

Discussion Status

The discussion is exploring the definitions and relationships between the variables involved. Some participants have provided guidance on reviewing the formula for the volume of a cone and the physical meaning of depth in this context. There is an ongoing examination of the assumptions made regarding the problem setup.

Contextual Notes

Participants note potential confusion regarding the units of measurement and the definitions of depth versus volume, which are critical to understanding the problem. There is an emphasis on ensuring clarity in the physical interpretation of the quantities involved.

lionely
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Homework Statement


An inverted right circular cone of vertical angle 120 is collecting water from a tap at a steady rate of 18∏ cm^3/min. Find
a) the depth of water after 12min,
b) rate of increase of depth at this instant



Homework Equations





The Attempt at a Solution



All I know is that dV/dt = 18cm3/min
so shouldn't the depth after 12 mins be 12 * dv/dt?
 
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lionely said:
All I know is that dV/dt = 18cm3/min
so shouldn't the depth after 12 mins be 12 * dv/dt?
.. which would imply a depth of what, 216 cm3? Anything strike you as odd about that?
 
Well yeah that is way too much :S
 
lionely said:
Well yeah that is way too much :S
No, I meant depth measured in cm3 (!)
 
Depth would be dh/dt, h being that height
 
That would give you units of cm/min, which isn't the units of depth. Based on your answer, I'm not sure you understand what the word depth means in the context of this problem.

Why don't you start by looking up the formula for the volume of a cone? Sketch a picture and tell us how the variables in the formula relate to the physical quantities in this problem.
 
lionely said:
Depth would be dh/dt, h being that height
The depth of the water is the height of the surface measured from the point of the cone. So it's a distance, not a volume, not a rate. dh/dt would be the rate of change of the depth.
 

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