Volume of a Cube The volume V of a cube with sides of length x in. is changing with respect to time. At a certain instant of time, the sides of the cube are 7 in. long and increasing at the rate of 0.2 in./s. How fast is the volume of the cube changing (in cu in/s) at that instant of time?

Respuesta :

Answer:

Therefore the volume of cube is change at the 29.4 cube in./s at that instant time.

Explanation:

Formula

  • [tex]\frac{dx^n}{dx} =nx^{n-1}[/tex]

Cube :

The volume of a cube is = [tex]side^3[/tex]

The side of length is x in.

Then volume of the cube is (V) = [tex]x^3[/tex]

∴ V = [tex]x^3[/tex]

Differentiate with respect to t

[tex]\frac{d}{dt}(V)=\frac{d}{dt} (x^3)[/tex]

[tex]\Rightarrow \frac{dV}{dt} =3x^2\frac{dx}{dt}[/tex]....(1)

Given that the side of the cube is increasing at the rate of 0.2 in/s.

i.e [tex]\frac{dx}{dt} = 0.2[/tex]  in/s.

And the sides of the cube are 7 in i.e x= 7 in

Putting [tex]\frac{dx}{dt} = 0.2[/tex]  and  x= 7 in equation (1)

[tex]\therefore \frac{dV}{dt} =3 \times 7^2 \times 0.2[/tex]  cube in./s

       =29.4 cube in./s

Therefore the volume of cube is change at the 29.4 cube in./s at that instant time.

The volume of the cube is changing at the rate of 29.4 in³/s.

Time derivative:

The rate of change of the sides of the cube is 0.2 in/s, which can be mathematically represented as :

[tex]\frac{dx}{dt}=0.2 \;in/s[/tex]

Now the volume of the cube is given by:

V = x³

If we take the time derivative of the above equation then it gives the rate of change of volume with time, so:

[tex]\frac{dV}{dt}= \frac{d}{dt}x^3\\\\ \frac{dV}{dt}= 3x^2\frac{dx}{dt}[/tex]

At the instant x = 7 in, the rate of change of volume will be:

[tex]\frac{dV}{dt}= 3\times7^2\times0.2\;in^3/s\\\\\frac{dV}{dt}=29.4\;in^3/s[/tex]

So the volume is changing at 29.4 cubic inches per second.

Learn more about differential equation:

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