posted by danny .
A variable-speed drill, initially turning at 500 rpm, speeds up to 1300 rpm in a time interval of 0.8 s. What is its average rotational acceleration?
This is just like linear acceleration, but going around. It's just a speed, velocity is measured in rotations/sec instead of meters/sec.
So, since the speed of the drill changed from 500-1300rpm, the change was 800rpm = 800/60 = 13.33 rot/sec.
That took 0.8s, so the average acceleration is
(13.33rot/s)/(0.8s) = 16.66 rot/s^2