问题
不定项选择
用轻弹簧竖直悬挂质量为m的物体，静止时弹簧伸长量为L。现用该弹簧沿斜面方向拉住质量为2m的物体，系统静止时弹簧伸长量也为L。斜面倾角为30°，如图所示。则物体所受摩擦力
A．等于零
B．大小为mg/2，方向沿斜面向下
C．大小为
mg，方向沿斜面向上
D．大小为mg，方向沿斜面向上
答案
答案：A
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用轻弹簧竖直悬挂质量为m的物体，静止时弹簧伸长量为L。现用该弹簧沿斜面方向拉住质量为2m的物体，系统静止时弹簧伸长量也为L。斜面倾角为30°，如图所示。则物体所受摩擦力
A．等于零
B．大小为mg/2，方向沿斜面向下
C．大小为mg，方向沿斜面向上
D．大小为mg，方向沿斜面向上
答案：A
| 从方框中选择适当的词并用其适当的形式填空。 | |
On the way to the Shancheng Theater, Rain knocks into (撞上) an old man. Rain: Sorry, did I hurt you? Mr. Read: Oh, I'm OK. 1 worry about it, young man. You seem to be in a great hurry. Rain: Yes, I'm new here. I am 2 the Shancheng Theater. Could you tell me the way, please? Mr. Read: Certainly. Go down this street till you reach the second crossing (十字路口), then turn right and you 3 it. Rain: How far 4 it from here? Mr. Read: It's about three kilometers. Rain: I must get there as soon as possible, but how can I get there? Mr. Read: There is no bus to go there now. You had better 5 a taxi. Rain: I see. 6 a lot. Sorry for 7 you so much trouble. 1._____ 2._____ 3._____ 4._____ 5._____ 6._____ 7._____ |