A conical tank has a radius of 2 ft at the top and a height of 3 ft. If a liquid flows in a rate of 2 ft^3/min, how fast is the water level rising when it is 2 ft high?

Respuesta :

Answer:

0.358 ft/min

Step-by-step explanation:

Let's say r and h are the radius and height of the water, and R and H are the radius and height of the tank.

The volume of the water is:

V = π/3 r² h

Using similar triangles:

r / h = R / H

r = h R/H

Substitute:

V = π/3 (h R/H)² h

V = π/3 (R/H)² h³

Take derivative with respect to time:

dV/dt = π (R/H)² h² dh/dt

Plug in values:

2 = π (2/3)² (2)² dh/dt

2 = 16π/9 dh/dt

1 = 8π/9 dh/dt

dh/dt = 9/(8π)

dh/dt ≈ 0.358

The water is rising at approximately 0.358 ft/min.

The water is rising at approximately 0.358 ft/min.

Calculation of the water rising:

Here we assume r and h are the radius and height of the water, and R and H are the radius and height of the tank.

We know that

The volume of the water is:

[tex]V = \pi \div 3 r^2 h[/tex]

Now here we used similar triangles:

[tex]r \div h = R \div H\\\\r = h R\div H[/tex]

Now

[tex]V = \pi \div 3 (h R\div H)^2 h\\\\V = \pi \div 3 (R\div H)^2 h^3[/tex]

Now take the derivative with respect to time:

So,

[tex]dV\div dt = \pi (R\div H)^2 h^2 \\\\2 = \pi (2\div 3)^3 (2)^3\\\\2 = 16\pi \div 9\\\\1 = 8\pi \div 9\\\\dh/dt = 9\div (8\pi )[/tex]

≈ 0.358

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