4、如圖所示，甲、乙、丙三個(gè)相同的杠桿，所掛的物體受到的重力均為G，它們分別在方向如圖所示的力F1、F2、F3作用下處于平衡狀態(tài)，那么
A．F1=F2=F3 B．F1<F2<F3C．F1>F2>F3 D．F2>F3>F1
D

試題分析：三個(gè)圖中，阻力和阻力臂都相同，因此只需判斷動(dòng)力臂的大小即可判斷出拉力的大小關(guān)系．設(shè)杠桿的長(zhǎng)為S，由圖和杠桿的平衡條件知：
甲：
乙：
丙：
聯(lián)立上述三式，易求得：F1＜F3＜F2；
故選D．
點(diǎn)評(píng)：在相同的作用點(diǎn)上，不同的力的方向?qū)?yīng)著不同的力臂，這一點(diǎn)需要注意．
練習(xí)冊(cè)系列答案
相關(guān)習(xí)題

科目：初中物理 來源：不詳 題型：單選題

使用如圖所示的裝置勻速提起重物G，所用的拉力中，（    ）
A．F1最大B． F2最大C．F3最大D．一樣大

查看答案和解析>>

科目：初中物理 來源：不詳 題型：填空題

如圖中的起瓶器，它屬于    杠桿(填“省力”或“費(fèi)力”),它的支點(diǎn)是     (填A(yù)、B 、C或D)；若沿豎直方向用力開啟瓶蓋，在圖中      點(diǎn)用力最小(填A(yù)、B 、C或D)。

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

用滑輪組在豎直方向提起重物，要求拉力是物重的．且拉力的方向向下，請(qǐng)?jiān)谌鐖D所示的方框中畫出滑輪組的繞法(不計(jì)動(dòng)滑輪重、繩重及摩擦，要求滑輪的個(gè)數(shù)為最少)．

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

人體就像一部復(fù)雜的機(jī)器，包含許多物理知識(shí)。

(1)人體是______體(導(dǎo)／半導(dǎo)／絕緣)，人體的安全電壓_____________V；
(2)人的前臂如圖甲所示，是一個(gè)________(省力／費(fèi)力／等臂)杠桿，這個(gè)杠桿的好處是_____________；
(3)正常人的心臟推動(dòng)血液流動(dòng)的功率約為1.5W，那么在3s內(nèi)心臟做的功是__________J，這些功可把一個(gè)0.5N的雞蛋勻速舉高_(dá)___________m.

查看答案和解析>>

科目：初中物理 來源：不詳 題型：單選題

升國(guó)旗的旗桿頂端有個(gè)重要的裝置是（    ）
A．定滑輪B．動(dòng)滑輪C．滑輪組D．省力杠桿

查看答案和解析>>

科目：初中物理 來源：不詳 題型：單選題

如下圖所示的四種情景中，所使用的杠桿屬于費(fèi)力杠桿的是

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)，下列操作中能讓杠桿繼續(xù)保持平衡的是
A．將左右兩邊的鉤碼均向外移動(dòng)一格
B．在左右兩邊鉤碼的下方各加一個(gè)鉤碼，位置保持不變
C．將左右兩邊的鉤碼各去掉一個(gè)，位置保持不變
D．將左邊的鉤碼向里移動(dòng)一格，同時(shí)將右邊鉤碼去掉一個(gè)并保持位置不變

查看答案和解析>>

同步練習(xí)冊(cè)答案