题目

About five years ago, an American electrical engineer named Scott Brusaw and his wife Julie came up with the idea of putting solar panels on the ground rather than the roof. Then they began to develop the Solar Roadway. The Solar Roadway is an intelligent road that provides clean renewable energy using power from the sun while providing safer driving conditions, along with power and data delivery. They predict that the Solar Roadway will pay for itself through the generation of electricity along with other forms of income and that the same money that is being used to build and resurfac20．如图所示，一轻绳通过无摩擦的小定滑轮O与质量为mB的小球B连接，另一端与套在光滑竖直杆上质量为mA的小物块A连接，杆两端固定且足够长，物块A由静止从图示位置释放后，先沿杆向上运动．设某时刻物块A运动的速度大小为VA，加速度大小为aA，小球B运动的速度大小为VB，轻绳与杆的夹角为θ．则（　　）A．VB=VAcosθB．aA=$\frac{{m}_{B}gcosθ}{{m}_{A}}$-gC．小球B减小的重力势能等于物块A增加的动能D．当物块A上升到与滑轮等高时，它的机械能最大