如图14所示,质量 M =4 kg的小车长 L =1.4 m,静止在光滑水平面上,其上面右端静止一质量 m =1 kg的块(可看作质点),小车与木板间的动摩擦因数 μ =0.4,先用一水平恒力 F 向右拉小车.( g =10 m/s 2 .) 图14 (1) 若用一水平恒力 F =10 N,块与小车间的摩擦力为多大? (2) 块与小车间不发生相对滑动的水平恒力 F 大小要满足的条件? (3) 若用一水平恒力 F =28 N向右拉小车,要使滑块从小车上恰好滑下来,力 F 至少应作用多长时间?
【简答题】从方框中选择最佳选项完成对话,有两项多余。 A. what are you doing? B. This is Jack speaking. C. It's raining. D. How is it going? E. What's the weather like in your country? F. I am Jack. G. It's very cool in the water. A:...
【单选题】听力原文:Lucy Long time no see. How are you going? Kevin Good to see you again. Im busy with my final paper these days. Lucy Wow. How is that? Kevin Well, Professor Smith required me to research violence ...
A.
No real agreement on the action that needs to be taken.
B.
No complaints about American police serials.
C.
No complaints about Chinese kung fu violence films.
D.
No need to care about the consequences of violence on TV.