[填空题]
A 2.30-m-long pole is balanced verticalln 9x+21y sbvngy+prfy;x:*f( e wh ,:wudoyu2s on its tip. It starts to fall and its lower end does not slip. What will be the speed of the upper end of the pole just before it hits the ground? (o*ep y wyuf+2sw;:,xrf :dh u[Hint: Use conservation of energy.] $m/s$