如图所示，有n(n>6) 个相同的小物块(可视为质点)静止在倾角为θ的倾斜轨道上，物块与轨道间的动摩擦因数均为μ。每个物块的质量均为m ，相邻物块间的距离均为 l 。使第 1 个物块以某一初速度v0 沿轨道开始下滑， 在每次发生碰撞时物块都立即粘合在一起运动，且碰撞一直能持续下去，重力加速度为g。

(1)求第一次碰撞前瞬间小物块l的速度;

(2)设第 5 次碰擅前的瞬间运动物块的动能为Ek5，第 5 次碰撞过程中系统损失的机械能为 E 损 5，求 E 损 5和 Ek5 的比值。

用“大雨和小雨”让幼儿感受线条的力度和粗细，体现了美术教学中的()。用“大雨和小雨”让幼儿感受线条的力度和粗细，体现了美术教学中的()。

若 5条鱼的平均质量为 0.8kg, 其中 3条的质量分别为 0.75kg,0.83kg 和 0.78kg ，则其余 2 条的平均质量为_____kg.

阅读理解，根据短文内容判断正(T)误(F)。

It's Sunday morning. The students of Class 3 are giving their classroom a good cleaning.

Miss Huang, their teacher, is working with them. The children are busy. Some are carrying water;

some are cleaning the windows; others are sweeping the floor. Zhang Hua is putting up a map on the

wall. It is a map of China. Wang Fei and Wei Qing are mending some broken chairs. The children are.

listening to the radio while they are working. The classroom looks nice and bright after the cleaning.

The children are very happy. They go home for lunch at noon.

( ) 1. The children are playing in their classroom on Sunday morning.

( ) 2. Miss Huang, their mother, is working with them.

( ) 3. There is a map of China on the wall.

( ) 4. Two of them are repairing the broken chairs.

( ) 5. They are singing while they are working.