[填空题]
A marble of mass m and radius r rolls along tzf u54uag-6o bhe looped rough track of Fig. 8–58.f6 a54gbuo- zu.ga0 1hu1nub3 t)w zei What is the minimum value of the vertical height h that the marble must drop if it is to reach the highest point of the loogb 10ztn)a1. eiuwh 3up without leaving the track? Assume $r\ll R$ and ignore frictional losses. h = R