Step-by-step explanation:
Angular acceleration of the bar,
..........(1)
We need to find the angle in radians through which the bar turns in the first 4.69 s.
We know that,

is angular velocity
On integrating equation (1) wrt t

...............(2)
Also,

On integrating equation (2) wrt t as :



At t = 4.69 s


Hence, this is the required solution.