搜题请搜索小程序“爱下问搜题”
问题 不定项选择

如图所示，一木块以一定的初速度沿倾斜传送带从顶端开始向底端下滑。第一种情形：传送带保持静止，物体能匀加速下滑；第二种情形：让传送带沿图中虚线箭头所示的方向匀速运动，物体仍能匀加速下滑。设物体都从顶端下滑到底端，则两种情形相比较

[ ]

A．在第二种情形中，木块所受摩擦力将变大

B．在第二种情形中，木块的运动时间将变长

C．在第二种情形中，木块克服摩擦力所做的功将变大

D．在第二种情形中，系统产生的内能数值将变大

答案

答案：D

单项选择题

A little boy invited his mother to attend his school’s first teacher-parent meeting. To the little boy’s (1) , she said she would go. This (2) be the first time that his classmates and teacher (3) his mother and he felt (4) of her appearance. Although she was a beautiful woman, there was a severe sear (疤痕) that (5) nearly the entire right side of her face. The boy never wanted to (6) why or how she got the sear.At the meeting, the people were (7) by the kindness and natural beauty of his mother (8) the sear, but the little boy was still embarrassed (尴尬) and (9) himself from everyone. He did, however, get within (10) of a conversation between his mother and his teacher.The teacher asked (11) ," How did you get the scar on your face"The mother replied, " (12) my son was a baby, he was in a room that caught fire. Everyone was (13) afraid to go in because the fire was (14) , so I went in. As I was running toward his bed, I saw a long piece of wood coming down and I placed myself over him trying to protect him. I was knocked (15) but fortunately, a fireman came in and saved both of us. " She (16) the burned side of her face. "This scar will be (17) , but to this day, I have never (18) what I did. "At this moment, the little boy came out running toward his mother with tears in his eyes. He held her in his arms and felt a great (19) of the sacrifice (牺牲) that his mother had made for him. He held her hand (20) for the rest of the day.

第（1）空应选择（）

A．enjoyment     

B．disappointment 

C．surprise    

D．excitement
查看答案
判断题

补油回路经过滤器芯堵塞会造成采煤机不牵引。（）
查看答案