2025-2026学年北京海淀区八年级物理下册期中模拟试卷（含答案详解与评分标准）第321套

2025-2026学年北京海淀区八年级物理下册期中模拟试卷（含答案详解与评分标准）第321套学校：________________班级：________________姓名：________________考号：________________考试时间：120分钟满分：120分考试范围：八年级物理下册期中适用区域：北京海淀区注意事项：一、本试卷共三部分，26道题。选择题12题，共36分；填空题6题，共18分；解答题8题，共66分。二、答题前请填写学校、班级、姓名和考号。计算题应写出必要公式、代入过程和单位，文字说明要完整。三、本卷中未特别说明时，g取10N/kg，水的密度取1.0×10³kg/m³。作图题要求用力的示意图规范表示方向和作用点。四、请保持卷面整洁。选择题在答题栏内填写选项，填空题直接写在横线上，解答题写在预留区域内。常用关系式：G=mg,p=F/S,p=rho*g*h,Fb=rho*g*V,F1*l1=F2*l2。一、选择题（本大题共12小题，每小题3分，共36分。每小题只有一个选项符合题意）题号123456789101112答案1．下列估测最接近真实情况的是（）A．一名八年级学生受到的重力约为50NB．一本物理课本平放在桌面上对桌面的压强约为1PaC．教室中一张课桌的高度约为0.8mD．北京海淀区春季一次体育课中学生跑步时受到的空气阻力约为200N2．端午前后，学校科技节进行“纸桥承重”展示。把同一张纸分别做成平板形和拱形，拱形纸桥更不易被压弯，这说明力的作用效果与下列哪一因素有关（）A．力的大小B．力的方向C．力的作用点和物体的形状结构D．受力物体的温度3．关于惯性，下列说法正确的是（）A．速度越大的物体惯性越大B．静止的物体没有惯性C．质量越大的物体惯性越大D．物体受到平衡力作用时惯性消失4．下列实例中，主要为了减小摩擦的是（）A．篮球鞋底做成花纹B．自行车轴承中加入润滑油C．体操运动员上器械前在手上擦镁粉D．汽车轮胎表面刻有较深沟槽5．如图示意可用文字描述：同一块长方体橡皮，先平放在水平桌面上，再侧放在同一桌面上。两次橡皮对桌面的压力分别为F₁、F₂，压强分别为p₁、p₂。若平放时接触面积较大，则（）A．F₁<F₂，p₁<p₂B．F₁=F₂，p₁<p₂C．F₁=F₂，p₁=p₂D．F₁>F₂，p₁>p₂6．在同种液体中，关于液体压强的说法正确的是（）A．只与容器底面积有关B．只与液体总质量有关C．随深度增大而增大D．液体向下有压强，向侧壁没有压强7．下列现象能说明大气压存在的是（）A．茶壶嘴和壶身上端一样高B．用吸管能把饮料吸入口中C．水从高处流向低处D．船闸使船由低水位驶向高水位8．一个重为6N的金属块浸没在水中时，弹簧测力计示数为4.2N。该金属块所受浮力为（）A．1.8NB．4.2NC．6.0ND．10.2N9．在“探究二力平衡条件”的实验中，小车静止在水平桌面上，左右两边细线分别挂等质量钩码。下列做法不能直接说明“两个力必须作用在同一直线上”的是（）A．把小车转过一个角度后释放B．让左右钩码质量相等C．观察小车是否能保持静止D．使两细线对小车的拉力方向不在同一直线上10．小明用撬棒撬起石块。若支点到用力点距离为1.2m，支点到阻力作用点距离为0.2m，不计撬棒自重，要撬起重600N的石块，至少需要的动力约为（）A．50NB．100NC．300ND．3600N11．某同学把质量相同、底面积不同的两个圆柱形容器放在水平桌面上，分别装入相同高度的水。若两容器底面积分别为S和2S，则两容器底部受到水的压强之比、桌面受到的压力之比分别为（）A．1:1，约1:1B．1:1，大于1:1且小于1:2C．1:2，1:2D．2:1，1:212．如表是某小组记录的弹簧测力计下挂同一物块逐步浸入水中的数据。由数据可判断，物块从部分浸入到浸没过程中浮力变化的主要原因是（）浸入情况未入水部分浸入1部分浸入2浸没测力计示数/N5.04.43.73.2A．液体密度变大B．物块受到的重力变小C．排开水的体积变大D．水对容器底的压强变小二、填空题（本大题共6小题，每小题3分，共18分）13．同一弹簧受到拉力F与伸长量x的关系如下表。弹簧原长为8.0cm。当挂上2.0N钩码时，弹簧长度为________cm；在弹性限度内，弹簧受到的拉力每增大1N，伸长量增大________cm。拉力F/N01.02.03.0弹簧长度L/cm8.010.012.014.014．水池中某处水深0.50m，水的密度取1.0×10³kg/m³，g取10N/kg，则该处水产生的压强为________Pa；若潜水小球再下沉0.20m，所受水的压强将________（选填“增大”“减小”或“不变”）。15．一个重为8N的物块，用弹簧测力计悬挂后浸没在水中，测力计示数为5N，则物块受到的浮力为________N；物块排开水的重力为________N。16．轻质杠杆AB可绕O点转动，OA=20cm，OB=50cm。在A端挂重10N的物体，要使杠杆水平平衡，应在B端竖直向下施加________N的力；该杠杆属于________（选填“省力”“费力”或“等臂”）杠杆。17．小华用弹簧测力计水平拉同一木块在同一木板上做匀速直线运动，第一次木块上不加砝码，示数为1.6N；第二次在木块上加砝码，示数为2.4N。两次木块受到的滑动摩擦力分别为________N和________N；该实验说明接触面粗糙程度相同时，压力越大，滑动摩擦力越________。18．在校园安全宣传中，常提醒同学不要把书包带调得过细，因为书包对肩的压力一定时，受力面积越小，压强越________；大型载重汽车有很多轮子，是通过增大受力面积来________对路面的压强。三、解答题（本大题共8小题，共66分。请写出必要的文字说明、公式、计算过程和结论）19．（6分）按要求作图并说明。一个重为5N的小球用细线悬挂在天花板下静止。请在答题区域用文字说明画出小球受力示意图应包含的要素，并说明这两个力为什么是一对平衡力。答：________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________20．（7分）学校倡议“轻书包”。某同学书包总质量为6.0kg，双肩背带与两肩的总接触面积约为0.030m²；若他改用单肩背，接触面积约为0.010m²。g取10N/kg。求：（1）书包受到的重力；（2）双肩背时书包对肩的压强；（3）由计算结果说明为什么不提倡长时间单肩背重书包。答：________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________21．（8分）某小组探究“滑动摩擦力大小与哪些因素有关”。他们用同一木块、同一弹簧测力计，在水平面上匀速拉动木块，记录如下。请回答：（1）实验中为什么要匀速拉动木块？（2）比较1、2两次实验可得到什么结论？（3）比较2、3两次实验可得到什么结论？（4）若第4次在毛巾面上斜向上拉木块，能否直接与第3次比较得出结论？说明理由。次数接触面木块上砝码个数测力计示数/N1木板01.22木板22.03毛巾23.14毛巾22.7答：________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________22．（8分）在“探究液体内部压强特点”的实验中，小组使用压强计、盛水的透明水槽和盐水。实验记录如下表。请回答：（1）U形管两侧液面高度差越大，说明探头处液体压强如何变化？（2）分析1、2、3可得什么结论？（3）分析3、4可得什么结论？（4）第5次把探头朝向侧壁，U形管高度差仍接近6.0cm，这说明什么？次数液体探头深度/cm橡皮膜方向高度差/cm1水5向下2.02水10向下4.03水15向下6.04盐水15向下6.85水15向侧面6.1答：________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________23．（8分）小明测量一块合金的密度。他先用弹簧测力计测得合金块在空气中的示数为7.8N；再把合金块浸没在水中且不碰容器底，示数为6.8N。水的密度取1.0×10³kg/m³，g取10N/kg。求：（1）合金块受到的浮力；（2）合金块的体积；（3）合金块的密度；（4）若实验时合金块碰到容器底，测出的密度会偏大还是偏小？说明理由。答：________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________24．（9分）海淀某校科技社团制作了简易液压演示器。小活塞面积为4.0cm²，大活塞面积为80cm²，装置中充满水并可近似看作密闭液体。某同学在小活塞上竖直向下施加40N的力。求：（1）小活塞对液体产生的压强；（2）理想情况下大活塞受到的向上力；（3）若要使大活塞升起质量为70kg的模型车，不计活塞重和摩擦，仅靠40N的力是否足够？（4）实际演示时大活塞上升较慢，写出一个可能原因。答：________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________25．（10分）如图可用文字描述：一根轻质直杆AB可绕O点转动，OA=0.30m，OB=0.90m。在A端挂一个重为180N的器材箱，在B端竖直向下拉绳使杠杆水平平衡。（1）求B端所需拉力；（2）若改在B端斜向下拉，拉力与OB夹角变小，要保持平衡，拉力大小如何变化？说明原因；（3）若在A端再挂一个重60N的工具袋，B端竖直向下拉力至少为多少？（4）结合校园搬运器材，说明使用杠杆时必须注意的安全事项一条。答：________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________26．（10分）阅读材料，完成问题。科技馆中有一个“浮沉子”演示瓶：密闭塑料瓶中装满水，瓶内有一个小滴管，滴管中封有少量空气。用手挤压瓶壁时，水压增大，更多水进入滴管，滴管的总重力增大；松手后，滴管内空气膨胀，一部分水被排出，滴管又会上浮。某次实验中，滴管和其中空气、水的总体积可近似保持为12cm³，水的密度取1.0×10³kg/m³，g取10N/kg。回答：（1）滴管浸没时受到的浮力约为多少？（2）当滴管总重为0.10N时，它将上浮、下沉还是悬浮？（3）挤压瓶壁后，滴管总重变为0.13N，它将如何运动？（4）从力与运动关系角度说明浮沉子由静止开始下沉的原因。答：________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

参考答案、详解与评分标准一、答案速查与评分矩阵题号12345678910111213分值3333333333333答案CCCBBCBABBBC12.0；2.0题号14151617181920212223242526分值333336788891010答案要点5.0×10³；增大3；34；省力1.6；2.4；大大；减小见详解见详解见详解见详解见详解见详解见详解见详解客观题评分：选择题每题3分，选对得3分，错选、多选或不选得0分；填空题每题3分，每空分值按题内要点给分，单位或方向性错误按评分说明扣分。主观题按步骤给分，合理方法同样给分。二、选择题详解1．答案：C。解析：课桌高度约0.8m符合生活实际；八年级学生重力通常约500N；课本对桌面的压强远大于1Pa；跑步时空气阻力远小于200N。2．答案：C。解析：同一张纸做成不同结构后承重能力改变，说明力的作用效果与受力物体的形状结构以及力的作用点、分布有关。3．答案：C。解析：惯性是物体保持原来运动状态不变的性质，大小只与质量有关，静止和运动物体都有惯性。4．答案：B。解析：轴承中加入润滑油可使接触面分离或减小粗糙程度，从而减小摩擦；其余做法主要是增大摩擦。5．答案：B。解析：同一橡皮在水平桌面上，压力等于自身重力，两次相等；平放接触面积大，由压强与受力面积成反比可知平放压强小。6．答案：C。解析：同种液体内部压强随深度增大而增大，并且在同一深度向各个方向都有压强。7．答案：B。解析：用吸管吸饮料时，管内气压减小，外界大气压把饮料压入口中，能说明大气压存在。8．答案：A。解析：浸没时物块受重力、拉力和浮力，浮力等于空气中重力与水中示数之差，即6N－4.2N=1.8N。9．答案：B。解析：只让左右钩码质量相等，说明二力大小可相等，不能直接说明二力必须在同一直线上；转动小车并观察能否静止才可检验共线条件。10．答案：B。解析：根据杠杆平衡，动力×动力臂=阻力×阻力臂，F×1.2m=600N×0.2m，F=100N。11．答案：B。解析：液体深度相同且都是水，底部压强相同；大容器中水的重力更大，桌面压力为容器重与水重之和，因此压力之比大于1:1但小于1:2。12．答案：C。解析：同一物块逐渐浸入水中，液体密度不变，物块重力不变；示数减小表示浮力增大，根本原因是排开水的体积增大。三、填空题详解13．答案：12.0；2.0。解析：由表可知拉力2.0N时弹簧长度12.0cm；从0到1N、1到2N、2到3N，每增大1N长度增加2.0cm，即伸长量增加2.0cm。14．答案：5.0×10³；增大。解析：液体压强p=ρgh=1.0×10³×10×0.50=5.0×10³Pa；深度增加，水的压强增大。15．答案：3；3。解析：浮力F浮=G－F示=8N－5N=3N；根据阿基米德原理，浮力大小等于排开水所受重力。16．答案：4；省力。解析：杠杆平衡：10N×20cm=F×50cm，F=4N；动力臂大于阻力臂，为省力杠杆。17．答案：1.6；2.4；大。解析：木块匀速直线运动时拉力等于滑动摩擦力，故两次摩擦力分别为1.6N、2.4N；接触面相同，压力越大，滑动摩擦力越大。18．答案：大；减小。解析：压力一定时，受力面积越小，压强越大；多轮胎增大受力面积，可减小压强。四、解答题详解与评分标准19．答案要点：受力示意图应以小球为研究对象，在小球重心附近画出竖直向下的重力G=5N，沿细线方向竖直向上的拉力T；两力大小相等、方向相反、作用在同一物体上且在同一直线上，所以是一对平衡力。评分标准：画出或文字说明重力方向、大小2分；画出或文字说明拉力方向2分；说明二力平衡四个条件中的关键点2分。若只写“静止所以平衡”但未说明方向和同体，最多得1分。20．计算：书包重力G=mg=6.0kg×10N/kg=60N。双肩背时，p=F/S=60N/0.030m²=2.0×10³Pa。单肩背时，p=60N/0.010m²=6.0×10³Pa。单肩背受力面积变小，压强增大到双肩背的3倍，肩部局部受压更明显，因此不宜长时间单肩背重书包。关键公式：G=mg,p=F/S。评分标准：写出并求得重力60N得2分；正确代入双肩面积并求得2.0×10³Pa得3分；能比较单肩压强更大并联系健康说明得2分。单位缺失扣1分，不重复扣。21．答案要点：（1）匀速拉动时木块处于平衡状态，水平方向拉力大小等于滑动摩擦力，便于由测力计读数得到摩擦力。（2）1、2接触面相同，压力不同，示数由1.2N增至2.0N，说明接触面粗糙程度相同时，压力越大，滑动摩擦力越大。（3）2、3压力相同，接触面由木板变为毛巾，示数增大，说明压力相同时，接触面越粗糙，滑动摩擦力越大。（4）不能直接比较，因为第4次斜向上拉会改变木块对水平面的压力，变量不唯一。评分标准：说明匀速与二力平衡关系2分；得出压力影响结论2分；得出粗糙程度影响结论2分；指出第4次不能比较并说明变量不唯一2分。22．答案要点：（1）U形管高度差越大，探头橡皮膜受到的液体压强越大。（2）1、2、3液体相同、方向相同，深度越大，高度差越大，说明同种液体内部压强随深度增大而增大。（3）3、4深度相同、方向相同，盐水高度差更大，说明深度相同时，液体密度越大，压强越大。（4）同一深度处，水向侧面的压强与向下的压强接近，说明液体内部同一深度向各个方向都有压强且大小近似相等。评分标准：每问2分。第（4）问只写“侧面有压强”得1分，能写同一深度各方向均有压强且大小近似相等得2分。23．计算：合金块浮力F浮=7.8N－6.8N=1.0N。由F浮=ρ水gV排，且浸没时V物=V排，得V=1.0/(1.0×10³×10)=1.0×10⁻⁴m³。合金块质量m=G/g=7.8/10=0.78kg，密度ρ=m/V=0.78/(1.0×10⁻⁴)=7.8×10³kg/m³。若碰到容器底，容器底对合金块有支持力，弹簧测力计示数偏小，计算出的浮力偏大，体积偏大，密度会偏小。关键公式：Fb