14. A computer hard drive typically operates with a rotation speed of 7200 rpm (

Question

14. A computer hard drive typically operates with a rotation speed of 7200 rpm (revolutions per minute). In the first 175 ms the hard drive turns through 4 revolutions at a constant angular acceleration. It continues with that acceleration until it reaches its maximum angular speed. (i) What is the angular acceleration of the drive, in rad/s2? (ii) What is the time required for the drive to reach its maximum angular speed, in ms? (iii) How many total revolutions have been made while the drive is

Explanation / Answer

14) w = 7200*2*pi/60 = 753.6 rad/s



i) theta = (1/2)*alfa*t^2

alfa = 2*theta/t^2 = 1640.5 rad/s^2

ii) w = wo + alfa*t

w =0 +alfa*t

t = w/alfa = 459 ms

iii)

w^2- wo^2 = 2*alfa*theta

theta = w^2/(2*alfa) = 173 rad = 27.56 revolutions

4) v = r*w = 2.412 m/s

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