题目

When you go for a run outside, chances are that you’ll find litter all ① you. Do you just go past it, or do you stop and pick it up? If you choose the second, you’re part of the latest popular sport in the West: plogging. The word “plogging” is the Swedish phrase “ plocka upp”( pick up) and the English word “Jogging” (running slowly) put together. What a plogger needs is a rubbish bag and a pair of gloves to protect your hands. While collecting rubbish, ploggers learn to classify (分类)and deal with it correctly, too. Plogging seems simple but it does a lot of good to both（2012年2月湖南部分学校联考）如图所示，一轻绳上端系在车的左上角的A点，另一轻绳一端系在车左端B点，B点在A点正下方，A、B距离为b，两绳另一端在C点相结并系一质量为m的小球，绳AC长度为，绳BC长度为。两绳能够承受的最大拉力均为。求： （1）绳BC刚好被拉直时，车的加速度是多大? （要求画出受力图） （2）在不拉断轻绳的前提下，求车向左运动的最大加速度是多大?（要求画出受力图）