[填空题]
A 2.30-m-long pole is balanced v 3y(;ykdn (wcqertics,*g /ie rmbp+uaao(2 ally 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 jus *b(/asem goup +r2,iat before it hits the ground? [Hint: Use conservation of energy.] $m/s$