How much work is done by the motor in a CD player to make a CD spin, starting from rest? The CD has a diameter of 12.70 cm and a mass of 16.30 g. The laser scans at a constant tangential velocity of 1.150 m/s. Assume that the music is first detected at a radius of 20.90 mm from the center of the disk. Ignore the small circular hole at the CD's center.

Respuesta :

Answer:

Explanation:

Given

Diameter of CD [tex]d=12.70\ cm[/tex]

radius [tex]r=6.35\ cm[/tex]

mass of CD [tex]m=16.30\ gm[/tex]

Tangential velocity [tex]v_t=1.150\ m/s[/tex]

music detected at [tex]r'=20.90\ mm=2.090\ cm[/tex]

Moment of Inertia of disc [tex]I=\frac{mr^2}{2}[/tex]

[tex]I=\frac{16.30\times 10^{-3}\times (6.35\times 10^{-2})^2}{2}[/tex]

[tex]I=6.572\times 10^{-5} kg-m^2[/tex]

Work done is equal to change in kinetic Energy of CD

[tex]W=\Delta K[/tex]

[tex]W=\frac{1}{2}I\omega_f^2-\frac{1}{2}I\omega_i^2[/tex]

where [tex]\omega =[/tex]angular velocity

[tex]v_t=\omega \times r[/tex]

[tex]W=\frac{1}{2}\times 6.572\times 10^{-5}\left ( \left ( \frac{1.15}{0.0209}\right )^2-0\right )[/tex]

[tex]W=0.0994\ J[/tex]