hLet the angle next to theta be alpha.
Therefore, tan alpha= 100/ 100 sqrt 3 => alpha= 30 degrees.
Since, alpha is the alternate angle to the angle of A( velocity 20m/s) and the distance AB. Therefore, it’s also equal to 30 as well.
Breaking 20m/s into components- 20Sin 30( perpendicular to ab) and 20 cos 30( along ab). Similarly, breaking the 20m/s velocity on the lower end on AB into 20 Sin theta ( perpendicular to BA) and 20 Cos theta( along BA)
With respect to A, ball B will move in the line AB. Hence,
20 Sin30= 20 Sin theta
Therefore, theta= 30 degrees.
AB= square root (100)2+ ( 100* sqrt 3)2
AB= 200m
Using the distance times relation, t= s/v
t= 200/ 20 Cos30 + 20 Cos 30
t= 10/ sqrt 3 seconds