Math Problem Statement

It is given that a container is in the form of an inverted right circular cone with a base radius 4 cm and height 16 cm. The container is held vertically. Initially, the container is fully filled with water. Then the water pumped out from the container at a constant rate of 60 cm3/s. Let V cm3 and h cm can be the volume and the depth of water in the container respectively after t seconds.

Solution

Let's break this problem down and set up the relations we need to solve it.

Step 1: Volume of a cone

The container is in the shape of an inverted right circular cone. The volume VV of a cone is given by the formula: V=13πr2hV = \frac{1}{3} \pi r^2 h where:

  • rr is the radius of the base of the cone,
  • hh is the height (or depth in this context),
  • π\pi is the mathematical constant Pi (approximately 3.1416).

However, the radius of the water level decreases as the water level drops. Since the cone is similar to the full cone, the radius rr of the water surface at any depth hh is proportional to the depth hh. For the full cone, when h=16h = 16 cm, r=4r = 4 cm. Therefore, we can express the radius rr as a function of hh using the proportionality: rh=416=14\frac{r}{h} = \frac{4}{16} = \frac{1}{4} Thus, at any depth hh, the radius rr of the water is: r=h4r = \frac{h}{4}

Step 2: Volume as a function of depth

Now substitute this expression for rr into the formula for the volume: V=13π(h4)2h=13πh316V = \frac{1}{3} \pi \left(\frac{h}{4}\right)^2 h = \frac{1}{3} \pi \frac{h^3}{16} This simplifies to: V(h)=πh348V(h) = \frac{\pi h^3}{48} This gives the volume of water in the container as a function of the depth hh.

Step 3: Rate of change of volume

The water is being pumped out at a constant rate of 60 cm³/s. This means that the volume VV is decreasing over time at a rate of: dVdt=60cm3/s\frac{dV}{dt} = -60 \, \text{cm}^3/\text{s} We can use the chain rule to relate the rate of change of volume to the rate of change of depth hh: dVdt=dVdhdhdt\frac{dV}{dt} = \frac{dV}{dh} \cdot \frac{dh}{dt}

First, find dVdh\frac{dV}{dh} by differentiating the volume function V(h)=πh348V(h) = \frac{\pi h^3}{48}: dVdh=3πh248=πh216\frac{dV}{dh} = \frac{3\pi h^2}{48} = \frac{\pi h^2}{16}

Now, substitute into the chain rule: 60=πh216dhdt-60 = \frac{\pi h^2}{16} \cdot \frac{dh}{dt} Solving for dhdt\frac{dh}{dt}, we get: dhdt=60×16πh2=960πh2\frac{dh}{dt} = \frac{-60 \times 16}{\pi h^2} = \frac{-960}{\pi h^2} This gives the rate of change of the water depth hh with respect to time tt.

Step 4: Initial conditions and further analysis

  • At t=0t = 0, the container is fully filled, meaning h=16cmh = 16 \, \text{cm}.
  • The relationship between volume, depth, and time could be further analyzed by integrating the rate of change of hh with respect to time.

Let me know if you'd like to explore more detailed steps in solving for h(t)h(t) or specific questions about this setup!

Follow-up questions:

  1. How long does it take to completely empty the container?
  2. What is the depth of the water after 30 seconds?
  3. How does the rate at which the depth decreases change as the water level drops?
  4. How would the problem change if the cone had a different base radius or height?
  5. Could we solve for the time when the water depth reaches a specific value (e.g., 8 cm)?

Tip:

When working with related rates, always express all quantities in terms of a single variable before differentiating to avoid errors.

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Math Problem Analysis

Mathematical Concepts

Geometry (Volume of a Cone)
Calculus (Rate of Change, Related Rates)
Proportionality

Formulas

V = (1/3)πr²h (Volume of a cone)
r/h = 1/4 (Proportional relationship)
V(h) = (πh³)/48 (Volume of water as a function of depth)
dV/dt = -60 cm³/s (Rate of change of volume)

Theorems

Chain Rule (for relating rates)
Derivative of Power Rule (d/dh of h³)

Suitable Grade Level

Grades 11-12