试题与答案

如图所示,P为质量为m=1kg的物块,Q为位于水平地面上的质量为M=4kg的特殊

题型:计算题

题目:

如图所示,P为质量为m=1kg的物块,Q为位于水平地面上的质量为M=4kg的特殊平板,平板与地面间的动摩因数μ=0.02。在板上表面的上方,存在一定厚度的“相互作用区域”,区域的上边界为MN。P刚从距高h=5m处由静止开始自由落下时,板Q向右运动的速度为v0=4m/s。当物块P进入相互作用区域时,P、Q之间有相互作用的恒力F=kmg,其中Q对P的作用竖直向上,k=21,F对P的作用使P刚好不与Q的上表面接触。在水平方向上,P、Q之间没有相互作用力,板Q足够长,空气阻力不计。(取g=10m/s2,以下计算结果均保留两位有效数字)求:

(1)P第1次落到MN边界的时间t和第一次在相互作用区域中运动的时间T;

(2)P第2次经过MN边界时板Q的速度v;

(3)从P第1次经过MN边界到第2次经过MN边界的过程中,P、Q组成系统损失的机械能△E;

(4)当板Q速度为零时,P一共回到出发点几次?

答案:

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参考答案:E

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