Answer:
4.25 s
Step-by-step explanation:
Given:
angular acceleration'α'= 1.8 rad/s²
angle 'θ'= 45 rad
time 't'= 4s
initial angular velocity '
'=0

as we know that,
θ=
t +

45 = 4
+ (0.5 x 1.8 x 16)
45- 14.4 = 4

30.6 = 4

= 7.65

Next is to find t by using the equation
=
+

7.65= 0 + (1.8)

= 7.65/1.8
= 4.25 s
Therefore, At the start of 4s interval the motion is at 4.25 second