A particle is projected from horizontal making an angle of 530 with initial velocity of 100 ms-1. The time taken by the particle to make angle 45° from horizontal is

Component (100 cos 530) 60 ms-1 will remain unchanged.Velocity will make 450 with horizontal when vertical component also becomes ± 60 ms-1.Using  v=u+a t   (In vertical direction)         +60=80+(-10)t1∴  t1=2 s⇒-60=80+(-10)t2∴  t2=14 s