英语周报初二外研版2019至2022答案

4.D【解析】刚滑上传送带时,物块做匀减速直线运动,速度减为0的位移x29m,可知物块到达传送带最右端之前已经减速为0,返回时先加速后匀速,再次回到出发点的速度与传送带速度相同,为4m/s,方向向左,因此物块离开传送带时的速度大小为4m/s,A项错误:由A项的分析可知,物块先向右做匀减速直线运动,再向左做匀加速直线运动,最后做匀速运动,所以摩擦力先做负功,再做正功,B项错误;物块所受摩擦力的冲量等于物块的动量变化量,取向右为正方向,物块的速度由向右的6m/s变为向左的4m/s,可知动量变化量为△P=-mmv=-10kg·m/s,由动量定理知物块所受摩擦力的冲量大小为10N·s,C项错误物块向右做匀减速运动的时间=四=3,相对位移△-2s+w21m,物块向左做匀加速运动的时间t2==2s,相对位移△x=w4wg=4m,所以物块和传送带之间的相对位移Δx=△x+△x2=25m,因此摩擦产生的热量Q=pmg△x=50J,D项正确。

应用文写作Dear BryanI sincerely invite you to our home to celebrate the Spring Festival together. It Is the most importantraditional festival for Chinese people No matter how far away we are, we'll try to get home as it is a time iorfamily reunion. We'll cook a lot of traditional Chinese food, such as dumpling, fish, meat, chicken, vegeta blesand fruits. If it is convenient for you, you can join us in our great dinner on Spring Festivals Eve. You are sureto have a good timeAr midnight, we'll fire fireworks. The foilowing morning, we'll visit elderly family members and expressrespect to themLooking forward to your replYours,

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