如圖所示OA是起重機(jī)的吊臂，可繞O點(diǎn)轉(zhuǎn)動．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)）
3600，變小

試題分析：如圖可知，阻力是3000N，阻力臂是6m，動力臂是5m，根據(jù)杠桿的平衡條件，，，∴；
將吊臂緩慢拉起，使用A點(diǎn)升高2m的過程中，阻力臂減小，所以阻力×阻力臂變小，動力臂不變，所以動力變小。
點(diǎn)評：解決本題的關(guān)鍵是找到動力臂和阻力臂的大小，利用杠桿的平衡條件做題。
練習(xí)冊系列答案
相關(guān)習(xí)題

科目：初中物理 來源：不詳 題型：填空題

如圖所示，輕質(zhì)杠桿AB可繞固定點(diǎn)O在豎直平面內(nèi)自由轉(zhuǎn)動，A端用細(xì)繩通過滑輪懸掛著底面積為0.02m2的重物G。工人在B端施加一個(gè)大小為650N豎直向上的推力時(shí)，重物對地面的壓力恰好為零；當(dāng)推力變?yōu)?50N時(shí)，重物對地面的壓強(qiáng)為5×103Pa；當(dāng)重物對地面壓強(qiáng)為8×103Pa時(shí)，工人對地面的壓力為980N；則若當(dāng)重物對地面壓強(qiáng)為1.2×104Pa時(shí)，工人對地面的壓力為        N（繩重及輪與軸的摩擦不計(jì)）

查看答案和解析>>

科目：初中物理 來源：不詳 題型：計(jì)算題

某人用下圖所示的滑輪組勻速提升500N的重物所用的拉力F為200N，繩子自由端被拉了2m，在此過程中，

求：（1）拉力做的功
（2）滑輪組的機(jī)械效率
（3）滑輪組中動滑輪的重
（4）若現(xiàn)提升800N的重物時(shí)，滑輪組的機(jī)械效率又是多少？
（不計(jì)繩重和摩擦）

查看答案和解析>>

科目：初中物理 來源：不詳 題型：單選題

下圖中，屬于省力杠桿的是 （   ）

查看答案和解析>>

科目：初中物理 來源：不詳 題型：填空題

如圖是人抬獨(dú)輪車車把時(shí)的簡化示意圖，此時(shí)獨(dú)輪車相當(dāng)于一個(gè)      杠桿（選填“省力”或“費(fèi)力”）；若動力臂是阻力臂的3倍，物體和車總重G為1200N，抬起車把的力F為       N。                         

查看答案和解析>>

科目：初中物理 來源：不詳 題型：單選題

如圖所示，杠桿處于平衡狀態(tài)，則F的力臂是
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
A．OAB．OCC．ODD．FD

查看答案和解析>>

科目：初中物理 來源：不詳 題型：填空題

如圖，輕質(zhì)杠桿OA可繞O點(diǎn)轉(zhuǎn)動，OA=0.3米，OB=0.2米．A點(diǎn)處掛一質(zhì)量為2千克的物體G，B點(diǎn)處加一豎直向上的力F，杠桿在水平位置平衡，則物體G的重力大小為______牛，力F大小為_____牛．

查看答案和解析>>

科目：初中物理 來源：不詳 題型：實(shí)驗(yàn)題

羅珍和丹珍用圖甲所示的杠桿一起探究杠桿的平衡條件：

（1）實(shí)驗(yàn)前，應(yīng)使甲圖中的杠桿在______位置平衡，可以杠桿左端的平衡螺母向____調(diào)，或?qū)⒂叶说钠胶饴菽赶騙___調(diào)；調(diào)平衡后，丹珍在乙圖所示位置處掛上3個(gè)鉤碼，要使杠桿在水平位置平衡，應(yīng)在杠桿右端的_____點(diǎn)掛上2個(gè)鉤碼。
（2）如乙圖，用彈簧測力計(jì)在M位置和N位置用力使杠桿在水平位置處于平衡，彈簧測力計(jì)的示數(shù)將會變________，這是因?yàn)開_____________________________________。

查看答案和解析>>

科目：初中物理 來源：不詳 題型：應(yīng)用設(shè)計(jì)題

如圖是用開瓶扳手打開瓶蓋的示意圖，O為支點(diǎn)，畫出動力F1的力臂（l1）和阻力（F2）的示意圖。

查看答案和解析>>

同步練習(xí)冊答案