14.如圖所示,圓O鉛直而立,60de6ecae99a8.jpg均表一直徑,夾角為θ,則一物沿60de6f02c6715.jpg自A靜止下滑至B所需時間為沿60de6f3fdcd92.jpg自C靜止下滑至D時間之半,設60de6f71cc2d6.jpg表面均光滑,則cosθ=_______。60de6fbce568f.jpg