[填空题]
A hollow cylinder (hoop) is rolling on a horizontal surface aclj.wzls ( 4cp)+ag) jen6k+lt speed v=3azp,qeqq so7( rs1.i) 8b ot:a.3 $m/s$ when it reaches a 15 $^{\circ} $ incline. (a) How far up the incline will it go? $\approx$ m (round to one decimal place) (b) How long will it be on the incline before it arrives back at the bottom? s