Two cannons, aimed at each other, stand on roofs of two identical  (meaning same height) very tall buildings, 100 meters apart. Both  cannons are fired at the same time.  However, one cannonball is bigger  and so it is fired at 20 m/s, while the other cannonball is smaller and  so it is fired at 30 m/s. 
 a) Will the cannonballs hit each other?