正圆锥容器体积是:v = (1/3)(pi)r^2 h 按题意,水深与水面圆直径相等, r/h = (12/2) / 18 = 1/3, r = 1/3 h 题中正圆锥容器体积是:v = (1/3)(pi)(h/3)^2 h = (pi/27) h^3 dv / dh = (pi/9) h^2, dv = (pi/9) h^2 dh 正圆柱容器体积是:V = (pi)R^2 H 题中正圆锥容器体积是:V = (pi)(10/2)^2 H = 25pi H dV /dH = 25 pi, dV = 25 pi dH 已知当溶液在漏斗中深为12cm时,其表面下降的速率为1cm/min, 即: dv = (pi/9) h^2 dh = (pi/9)x12^2 x 1 dV = dv, 25 pi dH = (pi/9)x12^2 x 1, dH = 25 x 9 / 12^2 = 225 / 144 = 1.56 (cm/min) 此时圆柱形筒中溶液表面上升的速率为1.56 cm/min。