小孩拉老牛问题

【题】一条绳子一端拴住一头牛，中段在木桩上绕了n圈，小孩握住绳子另一端，老牛想挣脱用力为F，小孩至少用多大力f才能拉住老牛，已知绳子与木桩之间的摩擦系数为μ。 【解】如图，列一小段绳子横向和纵向平衡方程 � EMBED Equation.DSMT4 ��� � EMBED Equation.DSMT4 ��� � EMBED Equation.DSMT4 ��� � EMBED Equation.DSMT4 ��� � EMBED Equation.DSMT4 ��� � EMBED Equation.DSMT4 ��� � EMBED Equation.DSMT4 ��� � EMBED Equation.DSMT4 ��� � EMBED Equation.DSMT4 ��� _1426365426.unknown _1426365706.unknown _1426367163.unknown _1426365571.unknown _1426365610.unknown _1426365652.unknown _1426365457.unknown _1426365260.unknown _1426365364.unknown _1426365239.unknown