A wheel initially rotating at an angular speed of 1.2 rad/s turns through 34 revolutions during the time that it is subject to angular accelaration of .4 rad/s/s. How long did the accelaration last?

Question

A wheel initially rotating at an angular speed of 1.2 rad/s turns through 34 revolutions during the time that it is subject to angular accelaration of .4 rad/s/s.  How long did the accelaration last?

So I used theta=Wot+.5at^2.  converted rev to rad.  and set it up like a quadrtaic equation giving 1.2t+.2t^2-213.6 giving me t equals 13.4 seconds but that is not right??

drwls · Answer

34 rev = 213.6 rad is OK (1/2)*0.4 t^2 + 1.2 t -213.6 = 0 is OK The positive root is t = [-1.2 + sqrt(1.44 + 170.88)]/0.4 = 29.8 s You seem to have used the quadratic equation incorrectly.