a knight sits on a castle wall during a siege. to while away the time, he notes that boul- ders catapulted from below land on the top of his wall with a vertical velocity of 7.6 m/s. if he is 35 m above the catapult, what is the initial velocity of the boulders? the acceleration of gravity is 9.8 m/s2 . answer in units of m/s.