It was announced at the conference that a wildlife reserve ______in the years to come. A is founded B are being founded C was to be founded D had founded 答案:C如图所示,物体A重30N,用F等于50N的力垂直压在墙上静止不动,则物体A所受的摩擦力是_________N;物体B重30N,受到F等于20N的水平推力静止不动,则物体B所受的摩擦力是________N。
30 20
【解析】试题分析:A处于静止状态,属于平衡状态,所以受到的是平衡力.摩擦力与重力是一对平衡力,A的重力的大小为30N,所以摩擦力也是30N.
B处于静止状态,属于平衡状态,所以受到的是平衡力.摩擦力与推力是一对平衡力,推力的大小为20N,所以摩擦力也是20N.