[填空题]
Two stones are thrown vertically up at the same time. The firshr2ptq9: uev7-1jw wlhqx ,q0 t stone is yi p4ervjl5 iz;gl64-c(t zqi)(*y nuthrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity should tei4(czl)iiy pr-tq;nj6 v* l4z ug5y(he second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors. m/s
