A cannonball is fired horizontally from the top of a cliff. the cannon is at height h = 80.0 m above ground level, and the ball is fired with initial horizontal speed v0. assume acceleration due to gravity to be g = 9.80 m/s2 .assume that the cannon is fired at time t=0 and that the cannonball hits the ground at time tg. what is the y position of the cannonball at the time tg/2?