A balloon is being inflated mechanically in such a way that the volume is increasing at a constant rate of 15 cm3 /s. If the volume of the balloon was originally 30 cm3, determine the average rate of change of the volume of the balloon with respect to the radius of the balloon, to the nearest centimetre cubed per centimetre, between 0 s and 10s, and between 10 s and 20 s.Discuss the following question:Is the rate of change of volume with respect to radius constant?

Respuesta :

The magnitude of the volume of the balloon increases at a faster rate than

the radius of the balloon.

  • The rate of change of the volume of the balloon with respect to radius is not  constant.

Reasons:

The rate at which the volume of the balloon is increasing, [tex]\dfrac{dV}{dt} = 15 \ cm^3/s[/tex]

The initial volume of the balloon, V = 30 cm³

The rate of change of the volume of the balloon with radius is given as follows;

[tex]\dfrac{\Delta V}{\Delta r}= \dfrac{V_2 - V_1}{r_2 - r_1}[/tex]

[tex]Volume \ of \ the \ balloon, \ V = \dfrac{4}{3} \cdot \pi \cdot r^3[/tex]

[tex]V = 30 + \dfrac{dV}{dt} \times t[/tex]

∴ V = 30 + 15·t

At t = 0, V = 30 cm³

Where;

[tex]r =\sqrt[3]{ \dfrac{3 \cdot V}{4 \cdot \pi} }[/tex]

When V = 30

  • [tex]r =\sqrt[3]{ \dfrac{3 \times 30}{4 \cdot \pi} } \approx 1.93[/tex]

The radius, r ≈ 1.93 cm.

At t = 10 s., we have;

V = 30 + 15 × 10 = 180

  • [tex]r =\sqrt[3]{ \dfrac{3 \times 180}{4 \cdot \pi} } \approx 3.5[/tex]

At t = 20 s., we have;

V = 30 + 15 × 20 = 330

  • [tex]r =\sqrt[3]{ \dfrac{3 \times 330}{4 \cdot \pi} } \approx 4.29[/tex]

Therefore;

Between 0 s. and 10 s., we have;

  • [tex]\dfrac{\Delta V}{\Delta r}=\dfrac{180 - 30}{3.5-1.93} \approx 96[/tex]

Rate of change of the volume of the balloon with respect to the radius of the balloon to the nearest centimeter, between 0 s and 10 s is 96 cm³/cm.

Between 10 s. and 20 s., we have;

  • [tex]\dfrac{\Delta V}{\Delta r}=\dfrac{330 - 180}{4.29 - 3.5} \approx 190[/tex]

Between 10 s. and 20 s. the rate of change is approximately 190 cm³/cm.

Therefore;

The rate of change of the volume of the balloon with respect to radius is not constant, but increases as the volume of the balloon increases.

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