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已知合力的大小和方向求兩個(gè)分力時(shí),下列說(shuō)法中正確的是(           )   

    A.  若已知兩個(gè)分力的方向,分解是唯一的

    B.  若已知一個(gè)分力的大小和方向,分解是唯一的

    C.  若已知一個(gè)分力的大小及另一個(gè)分力的方向,分解是唯一的

    D. 此合力有可能分解成兩個(gè)與合力等大的分力

                                                                                                        

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如圖示,小物塊每次都從傾角為30°的長(zhǎng)為40米的光滑斜面頂點(diǎn)O由靜止釋放,斜面和光滑水平面AB之間由一小段長(zhǎng)度不計(jì)的光滑弧面連接.物塊由B點(diǎn)滑上水平傳送帶BC后又滑向傾斜傳送帶DE.CD間由長(zhǎng)度不計(jì)的光滑曲面連接.傳送帶粗糙,物塊和傾斜傳送帶DE間滑動(dòng)摩擦因數(shù)為0.5.傳送帶DE傾角為37°.當(dāng)傳送帶都靜止時(shí),物塊最高能滑到F點(diǎn)速度減為零.DF間距離為5米.求:                                                                                      

(1)傳送帶都靜止時(shí)小物塊由O點(diǎn)釋放運(yùn)動(dòng)到B點(diǎn)和C點(diǎn)速度大小分別是多少?                                                                                                                                      

(2)試分析開(kāi)動(dòng)兩傳送帶能否使從O點(diǎn)靜止釋放的物塊在傾斜傳送帶DE上滑動(dòng) 的最大高度低于F點(diǎn)?若能,應(yīng)該怎樣開(kāi)動(dòng)兩傳送帶?                                                                                                           

(3)應(yīng)該怎樣開(kāi)動(dòng)兩傳送帶才能使從O點(diǎn)靜止釋放的物塊在DE上上升的距離最大,其最大距離是多少?(設(shè)DE傳送帶足夠長(zhǎng))                                                                                                                       

(4)如果傳送帶DE長(zhǎng)度只有55米,傳送帶BC的速度滿足(3)條件.可以調(diào)節(jié)DE傳送帶的速度,那么DE傳送帶勻速運(yùn)行最大速度不能超過(guò)多少,才能使從O點(diǎn)靜止釋放的物塊不會(huì)沖出DE傳送帶.                                                            

                                                                                                                                     

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如圖示,一輕質(zhì)薄板AB放在光滑水平面上,小物塊m1=1kg,m2=2kg都放在薄板的中點(diǎn)O.整個(gè)裝置初態(tài)靜止.物塊和薄板間的摩擦因數(shù)都為0.2.某時(shí)刻兩物塊同時(shí)受到向左F1=4N、向右F2=10N的水平拉力作用.兩物塊分別向左右加速運(yùn)動(dòng)2秒,此時(shí)M1恰好到達(dá)薄板左端A點(diǎn).求:                                                                   

(1)兩物塊在2秒內(nèi)運(yùn)動(dòng)加速度和2秒末速度;                                                          

(2)輕質(zhì)薄板AB的長(zhǎng)度.                                                                                          

                                                                      

                                                                                                                                     

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質(zhì)量M=4kg的小車(chē)內(nèi)有一跨過(guò)定滑輪的輕繩兩端連接小物塊m1和m2.如圖示,m1=1kg,m2=2kg.m1和固定在小車(chē)上的水平輕質(zhì)彈簧連接.m2由細(xì)線OA懸在豎直車(chē)壁上的O點(diǎn).車(chē)在水平向右的拉力F作用下在光滑水平面向右做勻加速直線運(yùn)動(dòng).整個(gè)裝置相對(duì)靜止.繩AB段水平,BC段豎直.繩OA和豎直方向夾角為45°.彈簧壓縮量為10厘米.不計(jì)一切摩擦不計(jì)定滑輪質(zhì)量.(g=10m/s2)求:                                                                                  

(1)小車(chē)加速度;                                                                                                       

(2)彈簧勁度系數(shù)k;                                                                                                 

(3)拉力F大。                                                                                                       

                                                                          

                                                                                                                                     

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國(guó)慶節(jié)間小明燃放一禮花彈,已知該禮花彈從水平地面以初速度V0豎直向上射出.在空中運(yùn)動(dòng)3秒爆炸,它在爆炸前1秒內(nèi)發(fā)生位移大小為4米.不計(jì)空氣阻力,g=10米/秒2.求:                                                       

(1)禮花彈初速度V0和上升最大高度;                                                                      

(2)禮花彈爆炸前瞬間速度和離地面高度.                                                                

                                                                                                                                     

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某同學(xué)在“研究勻變速直線運(yùn)動(dòng)”的實(shí)驗(yàn)中,用打點(diǎn)計(jì)時(shí)器記錄了被小車(chē)拖動(dòng)的紙帶的運(yùn)動(dòng)情況,在紙帶上確定出A、B、C、D、E、F、G共7個(gè)計(jì)數(shù)點(diǎn),其相鄰點(diǎn)間的距離如圖1所示,每?jī)蓚(gè)相鄰的計(jì)數(shù)點(diǎn)之間的時(shí)間間隔為0.10s.                                                                                                                                        

                                                                                                                                                

(1)根據(jù)紙帶上各個(gè)計(jì)數(shù)點(diǎn)間的距離,計(jì)算打下B、C、D、E、F五個(gè)點(diǎn)時(shí)小車(chē)的瞬時(shí)速度,并將各個(gè)速度值填在下面的橫線上:(要求保留三位有效數(shù)字)                                                                              

vB=                                                                                 m/s,vC=          m/s,vD=        m/s,vE=              m/s,vF=                                                                m/s;

(2)以A點(diǎn)為計(jì)時(shí)零點(diǎn),將B、C、D、E、F各個(gè)時(shí)刻的瞬時(shí)速度標(biāo)在如圖2所示的坐標(biāo)紙上,并畫(huà)出小車(chē)的瞬時(shí)速度隨時(shí)間變化的關(guān)系圖線;                                                                                                  

(3)根據(jù)第(2)問(wèn)中在畫(huà)出的v﹣t圖線,求出小車(chē)運(yùn)動(dòng)的加速度為         m/s2.(保留兩位有效數(shù)字)                                                                                                                                 

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如圖1示,用A、B兩彈簧測(cè)力計(jì)拉橡皮條,使其伸長(zhǎng)到O點(diǎn)(α+β<                                                                                                                                     

(1)現(xiàn)保持A的讀數(shù)不變,而使夾角減小,適當(dāng)調(diào)整彈簧測(cè)力計(jì)B的拉力大小和方向,可使O點(diǎn)保持不變,這時(shí)B的示數(shù)FB和夾角β的變化應(yīng)是                                                                                                 

A.FB一定變大,夾角β一定變大                          B.FB一定不變    夾角β一定變大                                                   

C.FB一定變小                                                      夾角β一定變小   D.FB變大、不變、變小均有可能   夾角β變小                                                                                                                      

(2)如圖2所示是甲和乙兩位同學(xué)在做以上實(shí)驗(yàn)時(shí)得到的結(jié)果,其中哪一個(gè)比較符合實(shí)驗(yàn)事實(shí)?                                                                                                                                               

                                                                                                                                     

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有一塊橫截面為矩形的長(zhǎng)板,長(zhǎng)度在70cm與71cm之間,寬度在7cm與8cm之間.厚度在0.5cm與1cm之間.小華用直尺(最小刻度為mm)、卡尺(游標(biāo)為50分度)和千分尺(螺旋測(cè)微器)測(cè)量此板的長(zhǎng)度、寬度、厚度.下列使用器材和對(duì)應(yīng)讀數(shù)可能正確的是                                              (     )                                           

    A.  用米尺測(cè)長(zhǎng)度讀數(shù)為70.2cm

    B.  用卡尺測(cè)寬度讀數(shù)為7.23cm

    C.  用卡尺測(cè)寬度讀數(shù)為7.233cm

    D.  用千分尺測(cè)厚度讀數(shù)為0.6250cm

                                                                                                                                     

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如圖,水平地面上有斜面b,b上有一小物塊a;當(dāng)給a施加一個(gè)沿斜面向下的力F1時(shí),a沿斜面下滑,此時(shí)b受地面摩擦力為零.在物塊下滑過(guò)程中,再給物塊施加一豎直向下的作用力F2,在物塊繼續(xù)下滑過(guò)程中,斜面保存靜止.則(   )                                                                                                                               

                                                                                           

    A.  加施F2后,b受地面支持力和摩擦力都不變

    B.  加施F2后,b受地面支持力變大,摩擦力不變

    C.  加施F2后,b受地面支持力變大,摩擦力方向向右

    D.  加施F2后,b受地面支持力不變,摩擦力方向向左

                                                                                                                                     

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如圖所示,三塊重均為3N的完全相同的光滑棋子A        B             C,B和C疊放在一起由豎直彈簧支持,初態(tài)靜止.現(xiàn)將A由靜止放到B上.則在A放到B上瞬間.(g=10m/s2)(              )                            

                                                                                                                 

    A. A對(duì)B的壓力為2N  B.      B對(duì)C的壓力為3N

    C. B的加速度為5m/s2  D.     C的加速度為零

                                                                                                                                     

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