the unit vectors i and j are directed horizontally and vertically upwards respectively.] (4Ui+Uj)ms 9.6m 64m Figure 2 The point O is 9.6 m above horizontal ground. A small ball is projected with velocity (4Ui+ Uj)ms', where U is a positive constant, from the point O The ball first hits the ground 7 seconds later, at the point A The point A is at a horizontal distance of 64 m from O, as shown in Figure 2. . In an initial model the ball is modelled as a particle moving under gravity air resistance is ignored the ball has an initial speed of Ims Using this model, (a) show that UT=16 (b) find the value of V (c) State two improvements to the model, other than including air resistance, that would make the model more realistic.