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题目:如图1所示,在光滑的水平面上有一辆长L=1.0米的小车 A,A 上有一木块 B(大小不计可视为质点),A 与 B 的质量相等,B 与 A 的滑动摩擦系数为μ=0.05。开始时 A 静止,B 位于 A 的正中央以速度v_0=5.0米/秒向右运动。假设 B 与 A 的前后两壁碰撞是完全弹性的。求 B 与 A 的前、后壁最多能相碰多少次?从开始到 B 与 A 的最后一次碰撞时 A 运动的总距离是多少?此题选自《北京市海淀区1990年5月期中练习物理试卷》,本文略有改动。本人试用速度—时间图象即 v-t 图象很简单地解决了这一问题。我们知道,开始物体 B 向右运动,由于摩擦力的存在,A 被带动向右作加速运动,B 亦作减速运动,到 B 与A的右壁碰前,有 v_(B1)>v_(A1)。由于 A、B 质量相等且碰撞是完全弹性的,故碰后二者速度交换,得 v_(A′1)=v_(B1),
Topic: As shown in Fig. 1, on a smooth horizontal surface, there is a trolley A with a length L of 1.0 m. There is a wooden block B on A (the size does not count as particles). The quality of A and B is equal to that of B and A. The sliding friction coefficient is μ=0.05. At the beginning, A is stationary and B is located in the center of A and moves to the right at speed v_0=5.0 m/s. Assume that the collision between B and A’s front and back walls is completely elastic. Find out how many times the front and back walls of B and A can touch at most? What is the total distance of A movement from the start to the last collision between B and A? This question is selected from the May 1990 mid-term exercises in Haidian District, Beijing. “Physics Examination Paper,” this article has changed slightly. I tried the speed-time image or v-t image to solve this problem simply. We know that when object B starts to move to the right, due to the presence of friction, A is accelerated to the right, and B is also decelerating. Before B and A’s right wall meet, there is v_(B1)>v_(A1 ). Since the masses of A and B are equal and the collision is completely elastic, after the collision, the speeds of the two are exchanged to obtain v_(A’1)=v_(B1).