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2015届中考物理(陕西)总复习：微专题五+功、功率和机械效率的计算.pdf

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1、微专题五功、功率和机械效率的计算一、利用滑轮组提升物体利用滑轮组提升物体，分三种情况：1理想情况：不计动滑轮重力、不计绳重和绳与轮之间的摩擦，即 W额0，FG物n，1，GhFs。2半理想情况：考虑动滑轮的重力，不计绳重和绳与滑轮之间的摩擦，即 W额G动h，F（G物G动）n，G物（G物G动）。3实际情况：考虑动滑轮的重力、绳重和绳与滑轮之间的摩擦(题目没有说明，表明要考虑)，即G物Fn，FG物n。【例】(2013，荆州)用如图所示的滑轮组提升重物，当作用在绳子自由端的拉力为100 N时，能匀速提起重力为240 N 的物体，不计绳重和摩擦，求：(1)动滑轮重力为多少？(2)若绕绳能承受的最大拉力为

2、200 N，则该滑轮组的最大机械效率为多大？【解析】(1)不计绳重和摩擦，知道拉力和物重的大小，利用 F13(G物G动)求动滑轮的重力；(2)已知绕绳能承受的最大拉力，根据 F13(G物G动)求出能承受的最大物重，再利用 W有用W总GhFsG3F求滑轮组的最大机械效率。【答案】(1)因为不计绳重和摩擦，所以 F13(G物G动)即 100 N13(240 NG动)，所以动滑轮的重力G动60 N。(2)因为绕绳能承受的最大拉力为200 N，所以 F最大13(G最大 G动)即 200 N13(G最大60 N)G最大540 N，则滑轮组的最大机械效率W有用W总G最大3F最大540 N3200 N90%

3、。【对应练习】1(2014，重庆)工人借助如图所示的装置，在 20 s时间内将重为700 N 的货物匀速提升了 4 m，已知他对绳子的拉力为500 N。该过程中，工人所用装置的机械效率为_70%_，工人对绳子拉力的功率为_200_W。2(2013，佛山)如图所示，物体 A 在大小为10 N 的拉力 F 作用下，以 0.3 m/s 的速度向右匀速运动(不计滑轮与细绳的摩擦及重力)，若物体 A 与桌面间的摩擦力为1 N，下列说法错误的是(D)文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y

4、9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX

5、5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y

6、9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX

7、5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y

8、9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX

9、5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y

10、9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9A拉力 F 做功的功率是3 W B物体 B 的质量是2.7 kg C物体 B 上升的速度是0.1 m/s D物体 A 运动 1 s，则物体 B 克服重力做功3 J 3(2013，襄阳)用如图所示的滑轮组提升货物，已知动滑轮重30 N，货物重 360 N，上升速度是0.3 m/s，拉力 F 的功率是180 W(不计绳重)。求：(1)滑轮组的机械效率。(2)货物上升3 m 的过程中，克服摩擦力做的功。解：(1)1 s 内货物升高的高度h0.3 m，W有Gh360 N0.3 m108 J，W总 P总t180 J，W有W

11、总108 J180 J 60%(2)货物上升3 m 的时间 thv3 m0.3 m/s10 s，W总 P总t180 W 10 s1 800 J，W有Gh360 N3 m1 080 J，提升动滑轮做的功W动G动h30 N3 m90 J，克服摩擦力做的功WfW总W有W动630 J 二、利用滑轮组水平拉物体利用滑轮组水平拉物体，此时克服物体受到的摩擦力做的功为有用功，与物重、滑轮重文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV

12、5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y

13、6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV

14、5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y

15、6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV

16、5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y

17、6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV

18、5Y2N7H3Y9无关；将上述公式中的G物换成 f 就行了。理想情况：W有fs，Ffn；实际情况：fFn，Ffn。【对应练习】4(2014，德阳)如图所示，在 20 N 的水平拉力F 作用下，重 200 N 的物体沿水平地面向左做匀速直线运动，物体与地面间的滑动摩擦力为48 N，则滑轮组的机械效率为_80%_；若物体的速度为0.2 m/s，则 1 min 内拉力做的功为_720_ J。5(2014，泰安)一辆质量是3.5 103 kg 的汽车不慎陷入泥泞地面，汽车司机组织人们用如图所示的滑轮组将汽车拖出。已知整个过程中，水平拉力F 是 1103N，汽车沿水平方向匀速移动了2 m，滑轮组的机械效

19、率为90%。求：(1)拉力 F 做的总功。(2)有用功为多大？(3)汽车受到的阻力大小。文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9

20、 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7

21、H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9

22、 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7

23、H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9

24、 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7

25、H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9解：(1)当汽车沿水平方向匀速移动了2 m 时，绳子末端移动6 m，根据 W总Fs1103N6 m6103 J(2)根据W有用W总，W有用W总90%6103 J5.4103 J(3)W有用 F拉s车，F拉W有用s车2.7103 N，由于车匀速运动，所以车受到的阻力fF拉2

26、.7103 N 6如图甲所示，重为 16 N 的物体 A 在拉力 F 的作用下，5 s内匀速运动了0.5 m。拉力 F 做的功随时间变化的图象如图乙所示。己知动滑轮重0.5 N，物体 A 在水平桌面上运动时受到的摩擦阻力f 为物重 G 的 0.25 倍。求：甲乙(1)拉力 F 的功率。(2)拉力 F 的大小。(3)克服绳重及摩擦所做的额外功占总功的比例。解：(1)由图象可知，5 s内拉力 F 做功 2.5 J，拉力做功的功率PWt2.5 J5 s0.5 W(2)由图象可知，s2h，绳末端移动速度v2v物2s物t20.5 m5 s0.2 m/s，做匀速文档编码:CE5A2Y6C1X9 HX5N4

27、Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档

28、编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4

29、Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档

30、编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4

31、Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档

32、编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4

33、Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9运动时，由 PFv 得 FPv0.5 W0.2 m/s2.5 N(3)克服绳重及摩擦做的额外功W额W总W有W动，由于物体A 做匀速运动，拉力 Ff0.25G0.2516 N4 N，则克服绳重及摩擦所做的额外功占总功的比例为W额外W总W总W有W动W总Fs绳 F s物G动s物Fs绳2.5 N20.5 m4 N0.5 m0.5 N 0.5 m2.5 N20.5 m110三、利用斜面提升物体利用斜面提升物体分

34、两种情况：1理想情况：不考虑机械自重和摩擦，沿斜面拉上去所做的功Fs 等于直接搬上去所做的功 Gh，即 FsGh。2非理想情况：考虑机械自重及摩擦，W有Gh，W总Fs，W额fs，W有W总GhFs。【对应练习】7(2014，呼和浩特)已知斜面倾角为30，斜面高为2 m。小兵同学用绳子沿斜面将重为 400 N 的木箱由斜面底端匀速拉到顶端。拉力大小为300 N，绳重不计。求：(1)小兵对木箱做的有用功。(2)斜面的机械效率。(3)斜面对物体施加的摩擦力。解：(1)W有Gh400 N2 m800 J(2)W有W总W有F2h800 J300 N22 m 66.7%(3)W额W总W有1 200 J800

35、 J400 J，则 fW额2h400 J22 m100 N 文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 Z

36、V5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2

37、Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 Z

38、V5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2

39、Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 Z

40、V5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9文档编码:CE5A2Y6C1X9 HX5N4Z9F2H1 ZV5Y2N7H3Y9

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关键词：: 2015 中考物理陕西复习专题功率机械效率计算

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