This question is an incomplete question, here is a complete question.
A dentist’s drill starts from rest. After 1.28 s of constant angular acceleration it turns at a rate of 24040 rev/min. Find the drill's angular acceleration in rad/s²
Answer : The angular acceleration of the drill is,

Explanation :
Formula used for angular acceleration of the drill is:

where,
a = angular acceleration
= initial angular velocity = 0
= final angular velocity =

t = time = 1.28 s
Now put all the given values in the above formula, we get:

Therefore, the angular acceleration of the drill is,
