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原题在2012年第30届伦敦奥运会体操男团中国队卫冕冠军,如图1所示张成龙在单杆比赛中正完成一个单臂回环动作,且恰好静止在最高点,设张成龙的重心离杆1.60米,体重大约56公斤,忽略摩擦力,认为张成龙做的是圆周运动,试求(1)张成龙在最低点应以多大的速度才能达到如图效果;(2)张成龙在最高、最低点时对杠的作用力.分析这道题第一问中答案建立了杆球模型.如图所示.质量集中在杆的中心,用重心的运动代替整个杆的运动.认为是质心P绕O点做圆周运动.最高点的临界速度v0=O最低点的速度为v,由动能定理知mg2l=12mv2可知:v=4槡gl,
Original title In 2012, the 30th London Olympic Games gymnastics men’s team defending champion of China, as shown in Figure 1 Zhang Chenglong in the single pole game is completing a single arm loop action, and just rest at the highest point, set the center of gravity of Zhang Chenglong 1.60 Meters, weighing about 56 kilograms, ignoring the friction that Zhang Chenglong is doing circular motion, try (1) Zhang Chenglong at the lowest point should be how much speed to achieve the effect as shown; (2) Zhang Chenglong at the highest point, the lowest point As shown in the figure, the mass is concentrated in the center of the rod, and the movement of the center of gravity is used to replace the movement of the whole rod. Circular motion. The highest point of the critical speed v0 = O lowest point of the velocity v, kinetic energy theorem know mg2l = 12mv2 know: v = 4 槡 gl,