The dimensions of a cylinder are changing, but the height is always equal to the diameter of the base of the cylinder. If the height is increasing at a speed of 3 inches per second, determine the speed at which the volume, V , is increasing (in cubic inches per second) when the height is 2 inches.

Respuesta :

Answer:

dV/dt  = 9 cubic inches per second

Explanation:

Let the height of the cylinder is h

Diameter of cylinder = height of the cylinder = h

Radius of cylinder, r = h/2

dh/dt = 3 inches /s

Volume of cylinder is given by

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

put r = h/2 so,

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

Differentiate both sides with respect to t.

[tex]\frac{dV}{dt}=\frac{3h^{2}}{4}\times \frac{dh}{dt}[/tex]

Substitute the values, h = 2 inches, dh/dt = 3 inches / s

[tex]\frac{dV}{dt}=\frac{3\times 2\times 2}{4}\times 3[/tex]

dV/dt  = 9 cubic inches per second

Thus, the volume of cylinder increases by the rate of 9 cubic inches per second.

The speed at which the volume "V" is increasing when the height is 2 inches is 9πin³/s

Given the data in the question;

Height is increasing at;[tex]\frac{dh}{dt} = 3in/s[/tex]

Height; [tex]h = 2 in[/tex]

We know that the Volume of a Cylinder can be calculated using the formula:

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

Where [tex]V[/tex] is the volume, [tex]\pi[/tex] is pie, [tex]r[/tex] is radius and [tex]h[/tex] is the height.

Given that the height is always equal to the diameter of the base of the cylinder.

Radius [tex]r[/tex] as a function of diameter is [tex]\frac{d}{2}[/tex], since d always equals h

Hence, Radius [tex]r = \frac{h}{2}[/tex]

So,  [tex]V = \pi r^2h = \pi (\frac{h}{2})} ^2h = (\frac{\pi }{4})h^3[/tex]

Now, lets differentiate both side with respect to time "t"

[tex]V = (\frac{\pi }{4})h^3[/tex]

[tex]\frac{dv}{dt} = (\frac{\pi }{4})3h^2\frac{dh}{dt}[/tex]

We substitute in our given values

[tex]\frac{dv}{dt} = (\frac{\pi }{4})3(2in)^2(3in/s)\\\\ \frac{dv}{dt} = (\frac{\pi }{4})36in^3/s\\\\\frac{dv}{dt} = 9\pi in^3/s[/tex]

Therefore, the speed at which the volume, V , is increasing when the height is 2 inches is 9πin³/s

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