A solid, uniform disk of mass M and radius a may be rotated about an axis parallel to the disk axis, at variable distances from the center of the disk.
What is Tmin, the minimum period of the pendulum?

Respuesta :

Answer:

the function varies linearly with the radius of the disk, so the smallest period is zero for a radius of zero centimeters

Explanation:

This system performs a simple harmonic movement where the angular velocity is given by

         w = √ k / I

Where k is the constant recovered from the axis of rotation and I is the moment of inertia of the disk

The expression for the moment of inertia is

           I = 1/2 m r²

Angular velocity, frequency and period are related

         w = 2π f = 2π / T

Substituting

             2π / T = √ k / I

             T = 2π √ I / k

             T = 2π √ (½ m r² / k)

             T = (2π √m / 2k)   r

 

We can see that the function varies linearly with the radius of the disk, so the smallest period is zero for a radius of zero centimeters

The minimum period of the pendulum Tmin is [tex]\mathbf{T_{min} = 2 \pi \sqrt{\dfrac{a^2}{ \Big ( \dfrac{ga}{\sqrt{2}}\Big)}} \ \ or \ \ 2 \pi\sqrt{ \dfrac{\sqrt{2a}}{g}}}[/tex]

The period of a pendulum refers to the time required to complete one single revolution or cycle.

Let consider the time period of the disk to that of bob of a pendulum, then, the period of the pendulum can be expressed as:

[tex]\mathbf{T(d) = 2 \pi \sqrt{\dfrac{a^2}{2gd}+\dfrac{d}{g} }}[/tex]

At minimum, the period of the pendulum needs to obey the condition that:

[tex]\mathbf{\dfrac{dT}{d(d)}=0}[/tex]

The above equation becomes:

[tex]\mathbf{\dfrac{d \Big( 2 \pi \sqrt{\dfrac{a^2}{2gd}+\dfrac{d}{g} }\Big )}{d(d)}=0}[/tex]

Taking the differentiation of the above equation with respect to d, we have:

[tex]\mathbf{d = \dfrac{a}{\sqrt{2}}}[/tex]

[tex]\mathbf{T_{min} = 2 \pi \sqrt{\dfrac{a^2}{2g \Big ( \dfrac{a}{\sqrt{2}} \Big)} + \dfrac{a}{g \sqrt{2}}}}[/tex]

[tex]\mathbf{T_{min} = 2 \pi \sqrt{\dfrac{a^2}{ \Big ( \dfrac{ga}{\sqrt{2}}\Big)}} \ \ or \ \ 2 \pi\sqrt{ \dfrac{\sqrt{2a}}{g}}}[/tex]

Learn more about the period of a pendulum here:

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