[填空题]
A 2.30-m-long pole is bff5me lusw67h;w c/4j alanced vertically on its tip. It starts to fall and i,v (* ( g;ummox3bjor/qw+ub qts lower end does not slip. What will be the speed of the upper end of the pole just before it hits the grom;(*,uq+ b qxrbjog(wmo/3vu und? [Hint: Use conservation of energy.] $m/s$