2022-2023 英语周报 八年级 新目标AHW 2答案

书面表达One possible versionDear DavidI have lived in America for a month. but I still find it difficult to adapt myself to a few things around me. I hope you would bekind enough to give me some help on the following problems.To begin with, I am not accustomed to the western food that tastes very different from Chinese food. Besides, I find I can't fit inwith others here because it is hard for me to catch up with what the local people say. What's worse. I have no friends here, so I feelI wonder how to deal with all these problems. I will be grateful if you can spare time to do me a favor. Please reply to me soon.Yours.Li Hua

21.BD【解析】由题意可知,没放滑块B时,木板A做匀速运动,即受力平衡,合力为零,设斜面的倾角为0,即2 mg sin0=p·2 mg cost,=tan0。放上滑块B后,对滑块B由牛顿第二定律可得 ng sin0=ma1,a1=gsin;对木板A由牛顿第二定律得2 mg sind0-3 mg cos=2ma2,可得a2gsin,即滑块B放在木板A的上表面之后,木板A将做匀减速直线运动,滑块B做匀加速直线运动,所以A错误;滑块B的动量为3mvo时,即vB==3v0,对B由匀变m速直线运动的公式可得1=2=30;对A由a1 sine2匀变速直线运动的公式可得t0=t0

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