A disk rotates about an axis through its center. point a is located on its rim and point b is located exactly one fifth of the way from the center toward the rim. what is the ratio of the angular velocity ωa to that of ωb, and the tangential velocity va to that of vb?

Respuesta :

[tex]r_{a}[/tex] = distance of point "a" from center of disk = r

[tex]r_{}[/tex] = distance of point "b" from center of disk = r/5

[tex]w_{a}[/tex] = angular velocity of point "a"

[tex]w_{b}[/tex] = angular velocity of point "b"

[tex]v_{a}[/tex] = tangential velocity of point "a"

[tex]v_{b}[/tex] = tangential velocity of point "b"

We know that angular velocity is independent of the distance from the center, hence the angular velocity is same at all points on the disk.

[tex]w_{a}[/tex] = [tex]w_{b}[/tex]

Ratio of angular velocity = [tex]\frac{w_{a}}{w_{b}}[/tex]

Ratio of angular velocity = [tex]\frac{w_{b}}{w_{b}}[/tex]

Ratio of angular velocity = 1

Tangential velocity is given as

v = r w

hence the ratio of tangential velocity is given as

Ratio of tangential velocity = [tex]\frac{v_{a}}{v_{b}}[/tex]

Ratio of tangential velocity  = [tex]\frac{r_{a}w_{a}}{r_{b}w_{b}}[/tex]

Ratio of tangential velocity =  [tex]\frac{r w_{b}}{(r/5)w_{b}}[/tex]

Ratio of tangential velocity = 5

The given locations of a radial length and a 5th of the radial length gives;

  • Ratio of the angular velocity at point a to point b is 1 : 1

  • Ratio of the tangential velocity at point a to point b is 5 : 1

How can the ratio of the velocities be found?

The angular velocity is given by the equation;

[tex] \omega \: = \frac{angle \: turned}{time} = \frac{1}{ period} [/tex]

Where;

A period, T = The time to complete a cycle

The angle turned by point a and point b at the same time, t, are equal, therefore;

[tex] \omega a = \omega b[/tex]

Which gives;

[tex] \frac{ \omega a}{ \omega b} = \frac{ \omega a}{ \omega a} = 1[/tex]

The ratio of the angular velocity,

[tex]{ \omega a}[/tex] to the angular velocity [tex]{ \omega b}[/tex] is therefore;

[tex]{ \omega a}[/tex] : [tex]{ \omega b}[/tex] = 1 : 1

Similarly, we have;

Tangential velocity, va = v × r

Tangential velocity, vb = v × r/5

va/vb = 5/1

va:vb = 5 : 1

Learn more about angular (rotational) velocity here:

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