题目

Sea Life Melbourne Aquarium (水族馆) The all－new Sea Life Melbourne Aquarium, situated in the heart of Melbourne's CBD, is one of Victoria's leading visitor attractions and an unforgettable outing for the whole family. Having 12 amazing zones of discovery, Sea Life Melbourne Aquarium is the very place that you cannot miss when you visit the city. ◆Opening Times Sea Life Melbourne Aquarium is open from 9：30 am until 6：00 pm every day of the year, including public holidays. Last admission is at 5：00 pm, one hour before closing. ◆Location (位置) Sea Life Melbourne Aquariu轻质弹簧原长为2L，将弹簧竖直放置在地面上，在其顶端将一质量为5m的物体由静止释放，当弹簧被压缩到最短时，弹簧长度为L。现将该弹簧水平放置，一端固定在A点，另一端与物块P接触但不连接。AB是长度为5L的水平轨道，B端与半径为L的光滑半圆轨道BCD相切，半圆的直径BD竖直，如图所示。物块P与AB间的动摩擦因数μ=0.5。用外力推动物块P，将弹簧压缩至长度L，然后放开，P开始沿轨道运动，重力加速度大小为g。（1）求弹簧压缩L时所存储的弹性势能Ep；（2）若P的质量为m，求P到达B点时速度的大小；（3）它离开圆轨道后落回到AB上的位置与B点之间的距离。