Question

A disk rotates about its central axis starting from rest and accelerates with constant angular acceleration. At one time it is rotating at 4.20 rev/s; 75.0 revolutions later, its angular speed is 23.0 rev/s. Calculate (a) the angular acceleration (rev/s2), (b) the time required to complete the 75.0 revolutions, (c) the time required to reach the 4.20 rev/s angular speed, and (d) the number of revolutions from rest until the time the disk reaches the 4.20 rev/s angular speed. _ unity rev/sa Units (a) Number 1 134.59 (b) Number 15.51 (c) Number 11.78 (d) Number12.49 unit " rad

Answer 1

a)

using 3rd equation of motion

a = ( w2^2 - w1^2) / ( 2 d)

a = ( 23^2 - 4.2^2)* ( 2* 3.14)^2 / ( 2*75* 2* 3.14)

a = 21.419 rad/s^2

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b)

t = w/t = 4.2* 2* pi / 21.419 = 1.232 s

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d) unit = revolution (or rev)