问题
单项选择题
质量为60kg的人站在水平地面上，用定滑轮装置将质量为m＝40kg的重物送入井中．当重物以2m/s2的加速度加速下落时，忽略绳子和定滑轮的质量及定滑轮的摩擦，则人对地面的压力大小为（g取10m/s2）（）
A.200N
B.280N
C.320N
D.920N
答案
参考答案：B
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质量为60kg的人站在水平地面上，用定滑轮装置将质量为m＝40kg的重物送入井中．当重物以2m/s2的加速度加速下落时，忽略绳子和定滑轮的质量及定滑轮的摩擦，则人对地面的压力大小为（g取10m/s2）（）
A.200N
B.280N
C.320N
D.920N
参考答案：B
| 用方框内词组的适当形式填空。 | |
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| 1. The news of the earthquake ______panic among people. 2. I'm sorry to tell you that the apples __ in our supermarket. 3. I won't leave the coffee shop until you______. 4. My car __ _ on the way and I had to have it repaired first. 5. My alarm clock didn't _______ this morning, so I got up late. 6. She always goes to school _ and is never late for class. 7. ______I got to school, the bell had already rung. 8. I took a shower, had some breakfast and_______ to the bus stop. |