A boy sees a ball going up and then back down through a window 2.45 m high. If the total time taken by the ball is 1 sec, the height above the window that the ball rises is

Here the ball is in sight for 1 sec. Thus the ball takes 1/2 second to go up across the window and 1/2 second to come down across it. Let h be the height that the ball rises above the window and t be the time taken to fall through h. Then the time taken to fall through the distance(h+2⋅45)m would be t+12 henceh=0×t+12gt2 or h=12gt2....(1)and (h+2⋅45)=0×t+12+12gt+122....(2)From eqs. (1) and (2)12gt2+2⋅45=12gt+122Solving, this equation, we gett=14sec∴ h=12×9⋅8×142=0⋅306m