Water is being pumped into an inverted conical tank at some constant rate. The tank has a height of 600 cm and the diameter of the tank across the top is 400 cm. If the water level is rising at a rate of 20 cm/min when the height of the water is 200 cm, find the rate at which water is being pumped into the tank. (Round your answer to the nearest integer.)
cm3/min

Respuesta :

Answer:

The water is being pumped at a speed of

[tex] \boxed{\bf \frac{10592000*\pi}{27}\;cm^3/min}[/tex]

Step-by-step explanation:

By congruence of triangles, the radius r of the cone base when its height is 200 cm satisfies the relation

r/200 = 400/600

(See picture attached)

So, r = 400/3 cm when the water is 200 cm high.

The volume of a cone with radius of the base = R is given by

[tex] \bf V=\frac{\pi R^2h}{3}[/tex]

So, the volume of water when it is 200 cm high is

[tex] \bf V_1=\frac{\pi* (400/3)^2*200}{3}=\frac{32000000*\pi}{27}\;cm^3[/tex]

One minute later, the height of the water is 200 cm + 20 cm = 220 cm

The radius now satisfies

r/220 = 400/600

and now the radius of the base is

r = 440/3

and the new volume of water is  

[tex] \bf V_2=\frac{\pi* (440/3)^2*220}{3}=\frac{42592000*\pi}{27}\;cm^3[/tex]

So, the water is raising (being pumped) at a rate (speed) of

[tex] \bf V_2-V_1=(\frac{42592000*\pi}{27}-\frac{32000000*\pi}{27})=\frac{10592000*\pi}{27}\;cm^3/min[/tex]

Ver imagen rodolforodriguezr

Using implicit differentiation, it is found that water is being pumped at a rate of 837758 cm³/min.

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The volume of a conical tank is given by:

[tex]V = \frac{\pi r^2h}{3}[/tex]

In which

  • r is the radius.
  • h is the height.

Applying the implicit differentiation, we have that:

[tex]\frac{dV}{dt} = \frac{\pi}{3}\left(2rh \frac{dr}{dt} + r^2\frac{dh}{dt}\right)[/tex]

We have that:

  • Height of 600 cm, thus [tex]h = 600[/tex].
  • Diameter of 400 cm, thus [tex]r = \frac{400}{2} = 200[/tex].
  • Water level rising at a rate of 20 cm/min, thus [tex]\frac{dh}{dt} = 20[/tex].
  • The radius is constant, that is, [tex]\frac{dr}{dt} = 0[/tex].

The rate at which water is being pumped into the tank is [tex]\frac{dV}{dt}[/tex], thus:

[tex]\frac{dV}{dt} = \frac{\pi}{3}\left(2rh \frac{dr}{dt} + r^2\frac{dh}{dt}\right)[/tex]

[tex]\frac{dV}{dt} = \frac{\pi}{3}\left(200^2(20)\right)[/tex]

[tex]\frac{dV}{dt} = 837758[/tex]

Rate of 837758 cm³/min.

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