[填空题]
A 2.30-m-long pole is balankqe6co4sppdmm ; .z: 2ced vertically on its tip. It starts to fall and its p zmq ec ;s4m.:k2d6pojtks+ffqyhk 2gh6)x,lq1 h 7+lower end does not slip. What will be the speed of the upper end of the pole just before it hits the ground? [Hint: Use confqk k7 jf)+t+2lhx61hq,syhg servation of energy.] $m/s$