7/ How much work is done by the motor in a CD player to make a CD spin, starting

Question

7/ 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 12.0 cm and a mass of 15.0 g. The laser scans at a constant tangential velocity of 1.15 m/s. Assume that the music is first detected at a radius of 18.5 mm from the center of the disk. Ignore the small circular hole at the CD's center.

8/ A mechanic turns a wrench using a force of 25.8 N at a distance of 13.6 cm from the rotation axis. The force is perpendicular to the wrench handle. What magnitude torque does she apply to the wrench?

9a/ As shown in the figure below, a 42.1-N force is applied to the outer edge of a door of width w = 1.34 m in such a way that it acts perpendicular to the door. Calculate the torque.

b/ Now, the 42.1-N force is applied to the outer edge of that door in such a way that it acts at an angle of ? = 42.9

Explanation / Answer

7) w = 1.15 x 1000/18.5 = 62.162 rad/s _______ I = 15 x .06^2/2 = .027 _____ Work = Iw^2/2 = 52.165 j _____________________ 8) Torque = F x R = 3.5088 J _______________________ 9) a) Torque = 42.1 x 1.34 = 56.414 Nm ____ b) Torque = 42.1 x 1.34 x sin42.9 = 38.402 Nm ____ c) Torque = 0, as line passes through axis ______________________ 10) apply moment equation about right end: 2.72 x 70.4 + 2.38 x 20.7 = l x 4.76 => l = 50.578 N ______ b) force by right cable = 70.4 + 20.7 - 50.578 = 40.521 N __________________________ 11) I = 163 x 2.11^2/2 = 362.84 ___ Torque = 13.8 x 2.11 x 2 = 58.236 Nm _____ Angular accelerartion = 58.236/362.84 = .1605 rad/s^2 ________________________ 12) 11.2 x 2.19 = 1.59 x w ___ w = 15.42 rad/s

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