專題二培優(yōu)點(diǎn)2力學(xué)三大觀點(diǎn)的綜合應(yīng)用

培優(yōu)點(diǎn)2力學(xué)三大觀點(diǎn)的綜合應(yīng)用目標(biāo)要求1.會(huì)在題中找出解題關(guān)鍵詞、臨界條件，從而理解題意并以此進(jìn)行解題。2.在力學(xué)計(jì)算題中會(huì)把多過程拆分為多個(gè)單過程，并會(huì)選擇合適的觀點(diǎn)進(jìn)行處理。力學(xué)三大觀點(diǎn)對(duì)比力學(xué)三大觀點(diǎn)對(duì)應(yīng)規(guī)律表達(dá)式選用原則動(dòng)力學(xué)觀點(diǎn)牛頓第二定律F合＝ma物體做勻變速直線運(yùn)動(dòng)，涉及運(yùn)動(dòng)細(xì)節(jié)勻變速直線運(yùn)動(dòng)規(guī)律v＝v0＋atx＝v0t＋eq\f(1,2)at2v2－v02＝2ax等能量觀點(diǎn)動(dòng)能定理W合＝ΔEk涉及做功與能量轉(zhuǎn)換機(jī)械能守恒定律Ek1＋Ep1＝Ek2＋Ep2功能關(guān)系WG＝－ΔEp等能量守恒定律E1＝E2動(dòng)量觀點(diǎn)動(dòng)量定理I合＝p′－p只涉及初末速度、力、時(shí)間，而不涉及位移、功動(dòng)量守恒定律p1＋p2＝p1′＋p2′只涉及初末速度，而不涉及力、時(shí)間例1(2023·江蘇卷·15)如圖所示，滑雪道AB由坡道和水平道組成，且平滑連接，坡道傾角均為45°。平臺(tái)BC與緩沖坡CD相連。若滑雪者從P點(diǎn)由靜止開始下滑，恰好到達(dá)B點(diǎn)?；┱攥F(xiàn)從A點(diǎn)由靜止開始下滑，從B點(diǎn)飛出。已知A、P間的距離為d，滑雪者與滑道間的動(dòng)摩擦因數(shù)均為μ，重力加速度為g，不計(jì)空氣阻力。(1)求滑雪者運(yùn)動(dòng)到P點(diǎn)的時(shí)間t；(2)求滑雪者從B點(diǎn)飛出的速度大小v；(3)若滑雪者能著陸在緩沖坡CD上，求平臺(tái)BC的最大長(zhǎng)度L。________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________例2(2023·浙江1月選考·18)一游戲裝置豎直截面如圖所示，該裝置由固定在水平地面上傾角θ＝37°的直軌道AB、螺旋圓形軌道BCDE、傾角θ＝37°的直軌道EF、水平直軌道FG組成，除FG段外各段軌道均光滑，且各處平滑連接。螺旋圓形軌道與軌道AB、EF相切于B(E)處。凹槽GHIJ底面HI水平光滑，上面放有一無動(dòng)力擺渡車，并緊靠在豎直側(cè)壁GH處，擺渡車上表面與直軌道FG、平臺(tái)JK位于同一水平面。已知螺旋圓形軌道半徑R＝0.5m，B點(diǎn)高度為1.2R，F(xiàn)G長(zhǎng)度LFG＝2.5m，HI長(zhǎng)度L0＝9m，擺渡車長(zhǎng)度L＝3m、質(zhì)量m＝1kg。將一質(zhì)量也為m的滑塊從傾斜軌道AB上高度h＝2.3m處靜止釋放，滑塊在FG段運(yùn)動(dòng)時(shí)的阻力為其重力的0.2倍。(擺渡車碰到豎直側(cè)壁IJ立即靜止，滑塊視為質(zhì)點(diǎn)，不計(jì)空氣阻力，sin37°＝0.6，cos37°＝0.8，重力加速度g取10m/s2)(1)求滑塊過C點(diǎn)的速度大小vC和軌道對(duì)滑塊的作用力大小FC；(2)擺渡車碰到IJ前，滑塊恰好不脫離擺渡車，求滑塊與擺渡車之間的動(dòng)摩擦因數(shù)μ；(3)在(2)的條件下，求滑塊從G到J所用的時(shí)間t。________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________(2023·江蘇省學(xué)業(yè)水平考試押題卷)如圖所示，傾角為α＝37°的斜面固定放置，B點(diǎn)下方粗糙，上方光滑，質(zhì)量為mQ＝3m的物塊Q放在B點(diǎn)時(shí)恰能不下滑，質(zhì)量為mP＝m的物塊P從斜面上A點(diǎn)由靜止釋放，A、B兩點(diǎn)間的距離為3m，P、Q間的碰撞為彈性碰撞，物塊P與斜面粗糙部分間的動(dòng)摩擦因數(shù)為0.5，一段時(shí)間后，物塊P與Q在斜面上發(fā)生第二次碰撞，不計(jì)碰撞時(shí)間和物塊的大小，設(shè)最大靜摩擦力等于滑動(dòng)摩擦力，sin37°＝0.6，重力加速度g取10m/s2。(1)求第一次碰撞后瞬間物塊Q的速度大??；________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________(2)求物塊P從靜止釋放到與物塊Q發(fā)生第二次碰撞所經(jīng)過的時(shí)間。____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________