A spherical raindrop evaporates at a rate proportional to its surface area with (positive) constant of proportionality k ; i.e. the rate of change of the volume exactly equals −k times the surface area. Write differential equations for each of the quantities below as a function of time. For each case the right hand side should be a function of the dependent variable and the constant k . For example, the answer to the first question should not depend on S or r . The volume of the drop: dV dt = Correct: Your answer is correct. The radius of the drop: dr dt =

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Answer:

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Step-by-step explanation:

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In this exercise we have to use our knowledge of volume, in this way it will be possible to calculate the spherical volume from the differential equations, so we will have to:

a)[tex]-6^{2\beta}k\pi ^{\beta}V^{2\beta}[/tex]

b) [tex]-K[/tex]

c) [tex]-4K\pi ^{1/2} S^{1/2}[/tex]

Knowing that the volume and sufrace area of the spherical raindrop of radius r is given by:

[tex]V=\frac{4}{3} \pi r^3\\S=4\pi r^2[/tex]

a) Given that the ratechange of the volume exactly equals -K times the surface area, so we have:

[tex]\frac{dV}{dT}=-KS\\=-K(4\pi r^2)\\=-4K\pi r^2\\=-4K\pi(r^3)^{2\beta}\\=-4K\pi(\frac{3V}{4\pi})^{2\beta}[/tex]

Knowing that:

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

Applying in the calculation before, that is:

[tex]=-4K\pi \frac{3^{2\beta}V^{2\beta}}{4^{2\beta}\pi ^{2\beta}} \\=4^{\beta}\pi ^{\beta}3^{2\beta}KV^{2\beta}\\= -2^{2\beta}3^{2\beta}K\pi^{\beta}V^{2\beta}\\=-6^{2\beta}K\pi^{\beta}V^{2\beta}[/tex]

b) The volume of the spherical raindrop of radius r is given by;

[tex]V=\frac{4}{3}\pi r^3 \\\frac{dV}{dt}= 4\pi r^2 \frac{dr}{dt}[/tex]

From part (a), we have:

[tex]\frac{dV}{dt}=-4K\pi r^2 \\4\pi r^2\frac{dr}{dt}=-4K\pi r^2 \\\frac{dr}{dt}=\frac{-4K\pi r^2}{4\pi r^2} = -K[/tex]

c) The volume of the spherical raindrop of radius r is given by:

[tex]V=\frac{4}{3}\pi r^3\\=\frac{4}{3}\pi (r^2)^{3/2}\\=\frac{4}{3}\pi \frac{S}{4\pi} ^{3/2}\\=\frac{\pi^{-1/2}S^{1/2}}{4}[/tex]

From the part (a):

[tex]\frac{\pi^{-1/2}S^{1/2}}{4}=-KS\\\frac{dS}{dt}=\frac{-4KS}{\pi^{-1/2}S^{1/2}}\\=-4K\pi^{1/2}S^{1/2}[/tex]

See more about volume at brainly.com/question/1578538

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