如图所示，传送带的倾角θ=37°，在电动机的带动下以v=4m/s的速率沿顺时针方向运行，在传送带的底端B有一离传送带很近的挡板P可将传送带上的物块挡住，在传送带的顶端A无初速地释放一物块，它与传送带间的动摩擦因数μ=0.5，A、B间的长度L=9m，物块与挡板碰撞前后物块的速度大小不变，方向相反，物块与挡板的碰撞时间极短．取g=10m/s²，sin37°=0.6，cos37°=0.8．求：

限价是国家对某些商品规定的价格极限，分为最高限价和最低限价两种。根据下图信息推断，相关结论正确的有（  ）

①最高限价会刺激消费、不利生产②最低限价一定高于市场均衡价格

③限价可弥补市场均衡价格的失灵④限价属于国家宏观调控行政手段

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      Hi, everyone! I am Paul Hawking, the trip leader for this weekend' s activity. It’s that time of the year again when the days are long and it is nice to sit outside and enjoy  some oysters(牡蛎).

      We plan to head out to the Mission Bay this Sunday for a beach picnic. You can buy fresh oysters at the Mission Bay Oyster Company and you just need to pay $6 to $l0 for each dozen, depending on the size. It' s on Sunday, June 30.

       We will meet at the Student Center at 9:00 a.m. and all go together. The driving time is one and a half to two hours, and the time of return is still uncertain. Come and join us in what must now be the 4th or 5th such trip for the Outing Club.

       The oyster farm has a small picnic area with chairs and barbecue grills (烧烤架). Bring some briquettes (煤球) if you would like to grill. Except for oysters, oysters and oysters, little is available there, so please bring your own food and drinks. And of course, if you have any special oyster recipes (食谱), bring them make them and share them!

       The weather forecast says it's going to be sunny and around 26°C this weekend. My telephone number is 408-896-3228. Please feel free to call me if you have any questions. Remember to finish your homework before we leave for the picnic.