[填空题]
A 2.30-m-long pole is balanced verbb9hxgh:.0y r ti a+40bluvplj oj*v90ically 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 poijl* jvpabv0 9+l 4u0ole just before it hits the ground? [Hint: Use conservation of energy.] $m/s$