题目

Are people happier in nature with blue skies overhead and fresh green grass underfoot? Could noisy streets, crowded with cars and people, make us unhappy?The possible mental health problems of city living affect a lot of people. The World Health Organization estimates(估计)that 56 percent of the world's population lived in urban areas in 2019. The WHO adds that that amount will increase to 66 percent by 2050. People often move to cities for better jobs and more cultural activities. But are they putting themselves at risk? Maybe. Experts at the American Psychiatry Association say that “natu7．如图所示，半径为R的半球形容器开口向上固定在水平地面上，球心与容器端口在同一水平面内，一质量为m的小物块从容器边缘A上方离A点h高处由静止落下，刚好贴着容器内壁并顺着内壁向下运动，在容器中向下运动时的速度大小不变，重力加速度为g，则下列说法正确的是（　　）A．物块沿容器内壁下滑过程中，受到的摩擦力大小恒定B．物块沿容器内壁下滑过程中，重力做功的功率先增大后减小C．物块第一次到容器最低点时，对容器的压力大小为（1+$\frac{2h}{R}$）mgD．物块从A滑到B的过程中，克服摩擦力做的功为mg（h+R）