题干

如图所示,重为20N的容器放在水平桌面上.容器的底面积S=2×102m2,高h=O.4m.当容器装满水时,容器对水平桌面的压强为4×103Pa,(ρ=1.0×103kg/m3)求:

(1)如图所示,水对容器底的压强多大?

(2)用一个弹簧测力计吊着一重为4N的物体,当物体全部浸没在该容器的水中时,弹簧测力计的示数为2.4N.该物体排开水的质量是多大?该物体的密度多大?

(3)容器中水受到的重力多大?

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答案(点此获取答案解析)

解:(1)水对容器底的GH压强:

P=ρgh=1.0×103kg/m3×9.8N/kg×0.4m=3.92×103Pa;

(2)①物体浸没在水中时,受竖直向下的重力G,竖直向上的浮力F

竖直向上的拉力F作用,处于平衡状态,由平衡条件可得:G=F+F,

物体受到的浮力F=G﹣F=4N﹣2.4N

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B

    John and Ann are from Dublin, Ireland. They've been friends since they were children. They lived in the same neighborhood when they were young and they went to the same university.

    Today John is a 34-year-old engineer. He works in the heart of Dublin. He is very busy and doesn't have much free time. He found a maid (女佣) to clean his house on Saturdays, but during the week he has to make the bed and tidy up his room. He must also wash the dishes. Sometimes he cooks a meal, but most of the time he stops at a restaurant near his home and buys a meal for dinner. He often arrives home very late. Luckily, his maid is quite professional and takes good care of the house. In just 6 hours, the house begins to shine, with a fresh look and clean air to breathe.

    Ann is 35 years old. She lives in a small village in Dublin. She works as a doctor at the village's health center. She starts working at 9 a.m. and finishes at 4 p.m. There is a half-hour lunch break at 12:30 p.m. After work, Ann has to pick up her two daughters from school. After they arrive home, the children do their homework while Ann prepares dinner. Her husband (丈夫) usually does part of the chores when he gets home. First he prepares the children's bath and then he washes clothes. Before dinner, he hangs up the clothes and then the children help him to lay the table (摆好餐具) and ... it's dinner time! After dinner, Ann's husband usually does the dishes while she tidies up the kitchen. When there is too much rubbish, she takes it out.

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