two boxes,m1=1.0kg with a coefficient of kinetic friction of 0.10,and m2=2.0kg with a coefficient of

题目

two boxes,m1=1.0kg with a coefficient of kinetic friction of 0.10,and m2=2.0kg with a coefficient of 0.20,are placed on a plane inclined at Θ=30.what acceletation does each box experience?If a taut string is connected to the boxes,with m2 initially farther down the slope,what is the acceleration of each box?If the initial configuration is reversed with m1 starting lower with a taut string,what is the acceleration of each box?

答案

第一问：a1=gsinΘ-u1gcosΘ=4.134;a2=gsinΘ-u2gcosΘ=3.268;
第二问：分两种情况,因为第一个箱子的加速度大,迟早会追上2号箱子；在追上之前,加速度和第一问一样,追上后,两个箱子挨在一起,考虑为一个整体；于是有：a1=a2=【(m1+m2)sinΘ-u1m1gcosΘ-u2m2gcosΘ】/（m1+m2）=3.557;
第三问中：一号箱子在下,绳子始终是绷直的,于是就可以将两个箱子考虑为一个整体和第二问中两个箱子挨在一起是一样的,加速度为：3.557.