题目

小华同学想用家里的体重计测量哑铃片的密度。他分别进行了如图甲、乙、丙所示的三次测量，对应的体重计示数分别为m1、m2、m3。若体重计单位为千克，水的密度用ρ表示，则丙图中哑铃片所受浮力表达式F浮=_____；该哑铃片的密度表达式ρ1=________。（结果用m1、m2、m3、ρ、g表示） 答案：【答案】（m3-m2）g 【解析】[1]图丙中，哑铃片被细线拉着浸没在水中时，水对哑铃片有向上的浮力，因力的作用是相互的，则哑铃片对水有向下的压力，且二力的大小相等，所以，与图乙相比，体重计受到压力的增加量等于哑铃片所受的浮力，则F浮=△F=（m3-m2）g ①；[2]物体浸没时排开水的体积等于物 补全文章(共5小题,每小题2分,满分10分)     根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。    A major source of teen stress is school exams, and test anxiety is not uncommon. When you recognize your teen is under stress, how can parents help your teen stay calm before an exam?    Be involved. Parents need to be involved in their teen’s work.  71   What they look for is your presence---to talk, to cry, or simply to sit with them quietly.Communicate openly with your teen. Encourage your teen to express his worries and fears, but don’t let them focus on those fears.    Help them get organized.  72   Together, you and your teen can work out a time-table in which she can study for what she knows will be on the test.    Provide a calm setting. Help your teen set up a quiet place to study and protect his privacy. Give them a nutritious diet. It’s important for your teen to eat a healthy,  balanced diet during exam times to focus and do her best. 73  If this happens,  encourage your teen to eat light meals or sandwiches. A healthy diet, rather than junk food, is best for reducing stress. 74Persuade your teenager to get some sleep and/or do something active when she needs a real break from studying. Making time for relaxation, fun and exercise are all important in reducing stress. Help your teen balance her time so that she will feel comfortable taking time out from studying to spend time with friends or rest. Show a positive attitude. 75  Your panic, anxiety and blame contribute to your teen’s pressure. Make your teen feel accepted and valued for her efforts. Most importantly, reassure your teen that things will be all right, no matter what the results are. A. A parent’s attitude will dictate their teen’s emotions. B. Exam stress can make some teens lose their appetite. C. They will only make the situation worse. D. Encourage your teen to relax. E. The best thing is simply to listen. F. Help your teen think about what she has to study and plan accordingly. G. Your teen may also make negative comments about themselves.