[填空题]
A 2.30-m-long pole is baldqkk0o.kfkrk4+ej;dc9 s6q7 msj0(bk a.7: 7nyo qbuanced vertically on its tip. It starts to fall and its lower end does not slip. What wilk7 (jumo0.7b:na qsybl be the speed of the upper end of the pole just before it hits the ground? [Hint: Use conservation of energy.] $m/s$