Can You Help? Starting From Rest, A 12-cm-diameter Compact Disk Takes 3.0 S To Reach Operating Angular Velocity 2000 Rpm.

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2 Answers

Westin Chan Profile
Westin Chan answered
ω = 2000*2π / 60 = 209.4 rad/s
Ang. Accel. ∆(ω /t) = 209.4 / 3 = 69.8 rad/s²

Torque T = I. ∆(ω /t) = (2.5^-5)(69.8) .. .. ►T = 1.745^-3 Nm
Oddman Profile
Oddman answered
Torque = (moment of inertia)*(angular acceleration)
  = (2.5*10-5kg m2)((2000 rev/min)/(3 s))(2π rad/rev)(1 min/(60 sec))
  = (2.5*10-5kg m2)(2000*2π/(3*60) rad/s2)
Torque = 5.56*10-4 N

If it is accelerating at a constant rate (which we assumed), the average speed of the disk over the 3 second period is 1000 rpm. In 3 seconds, the disk will make 1000 revolutions/(60 seconds)*3 seconds = 50 revolutions.

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