In foreign trade, is often used in consignment, auction and exhibition. It adapts to the business in fresh goods, antique, handcraft and calligraphy and painting.
【多选题】(2019· 全国卷 I·19) 如图,一粗糙斜面固定在地面上,斜面顶端装有一光滑定滑轮.一细绳跨过滑轮,其一端悬挂物块 N ,另一端与斜面上的物块 M 相连,系统处于静止状态.现用水平向左的拉力缓慢拉动 N ,直至悬挂 N 的细绳与竖直方向成 45°. 已知 M 始终保持静止,则在此过程中 ( )