physics
posted by HELP!!!! on .
A discus thrower (with arm length of 1.2 m) starts from rest and begins to rotate counterclockwise with an angular acceleration of 3.0 rad/s2.
(a) How long does it take the discus thrower's speed to get to 4.5 rad/s?
(b) How many revolutions does the thrower make to reach the speed of 4.5 rad/s?
revolutions
(c) What is the linear speed of the discus at 4.5 rad/s?
(d) What is the tangential acceleration of the discus thrower at this point?
(e) What is the magnitude of the centripetal acceleration of the discus thrown?
(f) What is the magnitude of the discus's total acceleration?

I will be happy to critique your thinking on this.

a) 4.5/3= 1.5 s
b) i'm still confused of how to get the number of revolutions
c) a=v^2/r the answer is 5.4 m/s
d) at=r alpha but we need to find alpha first to get at 
b, displacement= 1/2 angacceleration*time^2
c. Your answer is nonsense. Tangential velocty = angularvelocity*r
d.total acceleartion: find centripetal acceleration (v^2/r) That is inward. No tangentail acceleration is 3*r
those are at ninety degrees, add them as vectors (Pythagorean theorem_ 
i just want to find the number of revolutions , i know that 2 pi rad= 1 rev but how do we find that in this question.