问题 计算题

用细线AO、BO悬挂重物,如图所示,BO水平,AO与竖直方向成450角,若AO、BO能承受的最大拉力分别为10 N和5N,OC绳能承受的拉力足够大.为使细线不被拉断,重物G最大重力为多少?

答案

重物G的最大值为5N

以O为研究对象,0点受到拉力FA、FB和大小为G的拉力Fc作用,处于平衡状态.根据力的作用效果可将拉力Fc分解为FA'和FB',如图所示,则有FB'= FA'sin0,但由牛顿第三定律得FA=FA′,FB=FB',即FB =FAsinθ   

当FA ="10" N时,FB="7.07" N>5 N.由此可知,FB首先达到最大值.

BO绳拉力刚好达到最大值时,FB ="5" N,则此

时物重为mg=FC=FBcot450="5" N

所以,为使细线不被拉断,重物G的最大值为5N.

单项选择题 B型题
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