Rachel is blowing up a balloon so that the diameter increases at the rate of 10 cm/sec. At what rate must she blow air into the balloon when the diameter measures 4 cm

Respuesta :

Using implicit differentiation, it is found that she must blow air at a rate of 251.33 cm³/sec.

  • A balloon has a spherical format.

The volume of a sphere of radius r is given by:

[tex]V = \frac{4\pi r^3}{3}[/tex]

The radius is half the diameter, hence:

[tex]r = \frac{d}{2}[/tex]

[tex]r^3 = \frac{d^3}{8}[/tex]

[tex]V = \frac{4\pi d^3}{24} = \frac{\pi d^3}{6}[/tex]

Applying implicit differentiation, the rate of change of the volume is:

[tex]\frac{dV}{dt} = \frac{d^2 \pi}{2}\frac{dd}{dt}[/tex]

  • The diameter increases at the rate of 10 cm/sec, hence [tex]\frac{dd}{dt} = 10[/tex].
  • It is of 4 cm, hence [tex]d = 4[/tex]

The rate that she must blow air is:

[tex]\frac{dV}{dt} = \frac{d^2 \pi}{2}\frac{dd}{dt}[/tex]

[tex]\frac{dV}{dt} = \frac{4^2 \pi}{2}(10)[/tex]

[tex]\frac{dV}{dt} = 251.33[/tex]

She must blow air at a rate of 251.33 cm³/sec.

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