在圖中，A裝置是     滑輪（選填“定”或“動(dòng)”）．若用30N的拉力將旗幟勻速提升10m，則拉力所做的功為     J．

如圖，桿秤是一種測量工具。使用時(shí)，將待測物體掛在秤鉤A上，用手拎住秤鈕B或C（相當(dāng)于支點(diǎn)），秤砣D在秤桿E上移動(dòng)，當(dāng)桿秤水平平衡時(shí)就可以在秤桿上讀出讀數(shù)。

⑴從科學(xué)的角度來看，桿秤應(yīng)該是一種測量物理量      的工具。
⑵小明買5斤花生，但回家測量發(fā)現(xiàn)只有4.5斤。如果小販在秤盤上做手腳，則小販?zhǔn)?br />    _秤盤的質(zhì)量；如果小販在秤砣上做手腳，則小販?zhǔn)莀_     ___秤砣的質(zhì)量。(以上兩空選填增大或減小)

在學(xué)習(xí)了支點(diǎn)、動(dòng)力、阻力概念后，甲、乙兩小組繼續(xù)研究動(dòng)力對杠桿平衡的影響。他們將一個(gè)玩具“海寶”固定在杠桿一端的B點(diǎn)作為阻力，且保持阻力的大小、方向、作用點(diǎn)都不變，在杠桿的另一端用力使杠桿在水平位置平衡，并用測力計(jì)測出動(dòng)力的大小。實(shí)驗(yàn)中，甲小組每次都保持動(dòng)力在豎直方向、只改變動(dòng)力作用點(diǎn)的位置，分別如圖（a）所示；乙小組每次都保持動(dòng)力作用點(diǎn)的位置不變、改變動(dòng)力的方向（“動(dòng)力的方向”用OA連線跟動(dòng)力方向的夾角θ表示，且0°＜θ≤90°），分別如圖（b）所示；表一、表二是兩小組同學(xué)記錄的實(shí)驗(yàn)數(shù)據(jù)。

表一   甲小組				表二   乙小組
實(shí)驗(yàn) 序號	支點(diǎn)到動(dòng)力作用點(diǎn)的距離 S (厘米)	動(dòng)力的方向(夾角θ)	動(dòng)力的大小(牛)	實(shí)驗(yàn) 序號	支點(diǎn)到動(dòng)力作用點(diǎn)的距離 S (厘米)	動(dòng)力的方向 (夾角θ)	動(dòng)力的大小(牛)
1	5	90°	6	4	15	30°	4
2	10	90°	3	5	15	45°	2.8
3	15	90°	2	6	15	90°	2

（1）分析比較表一中第    列和第     列的實(shí)驗(yàn)數(shù)據(jù)可知：作用在杠桿一端的阻力不變時(shí)，要使杠桿平衡，在動(dòng)力方向不變（θ=90°）的情況下，支點(diǎn)到動(dòng)力作用點(diǎn)的距離S越大，動(dòng)力越小。
（2）分析比較表二中第三列與第四列的實(shí)驗(yàn)數(shù)據(jù)可知：作用在杠桿一端的阻力不變時(shí)，要使杠桿平衡，在動(dòng)力作用點(diǎn)不變的情況下， ______   _____。
（3）進(jìn)一步分析圖（b）所示的實(shí)驗(yàn)現(xiàn)象及表二中的實(shí)驗(yàn)數(shù)據(jù)，可以發(fā)現(xiàn)，作用在杠桿一端的阻力不變時(shí)，要使杠桿平衡，當(dāng)動(dòng)力作用點(diǎn)不變，動(dòng)力的方向改變以后，動(dòng)力的大小與____________    ____有關(guān)，且成反比關(guān)系。
（4）進(jìn)一步綜合分析表一與表二中的實(shí)驗(yàn)數(shù)據(jù)及相關(guān)條件，可得出的初步結(jié)論是：作用在杠桿一端的阻力不變時(shí)，影響杠桿平衡的因素是__    _和__    ___。

使用滑輪組肯定不能做到的是

A．既省力又改變力的方向

B．既省力又省距離

C．省力但不能改變力的方向

D．不省力但可以改變力的方向

如圖所示，杠桿處于平衡狀態(tài)，則F的力臂是
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               

A．OA

B．OC

C．OD

D．FD

下列工具在正常使用的過程中，可以看作費(fèi)力杠桿的是

下列測量工具沒有利用杠桿原理的是（　　）

如圖所示，我們在拖動(dòng)行李箱時(shí)一般先拉出行李箱上方的拉桿，這樣做的目的是為了

A．減小阻力臂，省力	B．增大阻力臂，省力
C．減小動(dòng)力臂，省力	D．增大動(dòng)力臂，省力

如圖所示，重為100N的物體A在水平拉力F的作用下，沿水平面以0.4m／s的速度作勻速直線運(yùn)動(dòng)，彈簧秤的示數(shù)為5N.不計(jì)滑輪、繩子、彈簧秤的重力，忽略繩子與滑輪間的摩擦。則物體A受到水平面的摩擦力為________N; 若物體A勻速運(yùn)動(dòng)2s，拉力F做功為________J,拉力F的功率為________W.

如圖所示OA是起重機(jī)的吊臂，可繞O點(diǎn)轉(zhuǎn)動(dòng)．在距O點(diǎn)6m遠(yuǎn)的B處吊有重3000 N的物體．為保證吊臂在水平位置平衡，則繞過定滑輪斜向下的拉力F為_____N.將吊臂緩慢拉起，使用A點(diǎn)升高2m的過程中，拉力變______（選填變大、變小或不變）．（繩重、吊臂重、摩擦均不計(jì)）