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

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