A projectile is thrown in the upward direction making an angle of 60° with the horizontal direction with a velocity of 150 ms-1. Then the time after which its inclination with the horizontal is 45° is

At the two points of the trajectory during projectile motion, the horizontal component of the velocity is same. Then150×12=v×12   or   v=1502 ms-1  Initially: uy=usin60°=15032 ms-1  Finally: vy=vsin45°=1502×12=1502 ms-1  But vy=uyy+ayt   or   1502=15032-10t∣ 10t=1502(3-1)   or   t=7.5(3-1)