Posted by Allie on Friday, October 7, 2011 at 5:51pm.
A dentist's drill starts from rest. After 3.30 s of constant angular acceleration it turns at a rate of 2.1x10^4 rev/min.
(a) Find the drill's angular acceleration.
rad/s2
(b) Determine the angle (in radians) through which the drill rotates during this period.
rad

Physics  drwls, Friday, October 7, 2011 at 6:58pm
(a) Divide the final angular velocity (in rad/s, NOT rpm) by the time interval.
(b) angle = (1/2)*(angular acceleration)*t^2
OR
(1/2)*(final angular velocity)*time 
Physics  Kels, Thursday, November 10, 2011 at 9:30pm
Why do you multiply by .5?

Physics  helper, Saturday, May 5, 2012 at 8:26pm
it is based off the equation:
displacement = (initial velocity)*(change in time) + 1/2(acceleration)*(change in time squared)
since that equation is linear, the equation recommended for this problem is:
"angle" = 0 + 1/2(acceleration)*(change in time squared)
that is how one gets the 1/2