[填空题]
Romeo is chucking pebbles gently up *trzo)n1h z+iz zm +z;to Juliet’s window, and he wants the pedu e z :1,+i5wo)ojjtubbles to hit the window with only a horizontal component of velocity. He is standing at the edge ofje+ wt,ji:do 1ozu )5u a rose garden 4.5 m below her window and 5.0 m from the base of the wall (Fig. below). How fast are the pebbles going when they hit her window? m/s