问题
选择题
.如图所示，物体重G＝10N，作用在物体上的力F＝40N，且F与墙壁垂直，这时墙壁受到的压力大小是（ ）
A．10N
B．40N
C．30N
D．50N
答案
答案：B
根据二力平衡的知识可以知道，竖直方向上的重力和摩擦力是一对平衡力，水平方向的压力与重力无关，墙受到的压力物体把由物体传过来的，等于物体受到的压力，等于40N．
故选B．
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.如图所示，物体重G＝10N，作用在物体上的力F＝40N，且F与墙壁垂直，这时墙壁受到的压力大小是（ ）
A．10N
B．40N
C．30N
D．50N
答案：B
根据二力平衡的知识可以知道，竖直方向上的重力和摩擦力是一对平衡力，水平方向的压力与重力无关，墙受到的压力物体把由物体传过来的，等于物体受到的压力，等于40N．
故选B．
It’s a sad and familiar voice that we often hear in big cities: “Can you spare some change?” Usually, when faced with that particular , I have feelings of guilt if I pass by giving a coin or two. I had that feeling in Venice while on a tour of Italy’s famous sites in 2006. I had taken refuge from the in a quiet café. Outside, there was an old woman kneeling on the hard, ancient paving stones, . Steady of tourists were walking past her. A young backpacker stood away from the crowd, drinking in the vistas（景观、景色）, but I noticed the young traveler was also the old woman. A tourist group walked along the street, the woman and walked on. group of tourists arrived and walked past the old lady. The backpacker watched everybody else went on their way, focused on the around them. Then, I was preparing to leave when I caught sight of the backpacker stepping forward and some money in the woman’s cup. He did this somewhat just before the arrival of another tourist group. As I , the leader of the group stopped and put some money in the cup. Having been shown the way, other tourists followed suit and some more coins to the cup. His work done, the young man walked over to the old beggar-woman, patted her on the shoulder and said, “I hope that a little.” I don’t know if the woman understood his English or what had just happened, but I did. I placed some money in the woman’s cup and continued my travels, after witnessing such a act of kindness.
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