2022英语周报sxj第60答案

20.BDPQ两点处弹簧弹力的大小相等,则由胡克定律可知P点的压缩量等于Q点的伸长量,由几何关系知PQ=dm3-3d,则小球位于P点时弹簧的压缩量为x=PQ=3对P点的小球由力的平衡条件可知mg=k,.解得k,选项A错误;当小球运动到P点时,假设小球甲的速度为v,此时物体乙的速度为零,又小球、物体和弹簧组成的系统机械能守恒则由机械能守恒定律得切g(=-0-mm53=m,解得=√÷m,选项B正确;小球由P到Q的过程弹簧的弹性势能先减小后增大,则小球甲和物体乙的机械能之和先增大后减小,选项D正确;由于小球在P和Q点处,物体乙的速度都为零,则物体乙重力的瞬时功率先增大后减小,选项C错误

ear jonaIm glad to hear from you and i d like to share withyou something about serving chopsticksi As you know, people in China are encouraged to useserving chopsticks, which are different from personal chopticks in shape and colour serving chopsticks are used totake food from shared dishes. You can add food to yourbowl with them, but never place them into your mouth oryour own bowlUsing serving chopsticks benefits everyone at tableFirst of all, it prevents diseases from' spreading while weare eating together. We can also use them to put food intoothers bowls, thus creating a pleasant and harmoniousdining atmosphereHoping you'l come to China to experience themfirst handYoourL i hua

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