搜题请搜索小程序“爱下问搜题”
问题 多选题

质量为m的物体在拉力F的作用下从静止出发以2g的加速度匀加速上升h，则（　　）

A．物体的机械能增加2mgh

B．物体的重力势能增加mgh

C．物体的动能增加Fh

D．F做功等于物体增加的动能加上物体增加的势能

答案

A、物体从静止开始以2g的加速度沿竖直方向匀加速上升，根据牛顿第二定律，有

F-mg=ma

解得：F=m（g+a）=3mg

根据重力之外的力做功量度重力势能的变化得：

△E=Fh=3mgh

所以物体的机械能增加3mgh．故A错误．

B、重力做功WG=-mgh

所以物体的重力势能增加mgh，故B正确．

C、根据动能定理，有

-mgh+Fh=Ek

解得Ek=-mgh+Fh=2mgh，故C错误

D、根据A选项分析，故D正确．

故选BD．

听力题

根据短文内容及首字母提示补全单词

Let me tell you something about our park. It’s not very big b  1 beautiful. Here’s the g 2 . We can go into the park form here. on the l  3 of it. There are two toilets. There is a c  4 on the right.  We can drink coffee or have meals there.  There is a big tree near it. in the tree, there are many b 5 . they are singing. In the m  6  of the park, there is a p  7  . There are many boys and girls on it. Some are flying kites, and others are dancing. They are h_ 8 _. Near the playground, there is a nice and big l _9__ . There are many b  10  in it, and we often read them there. 
查看答案
单项选择题

销售对企业的作用，下列不正确的说法是（）

A.销售是实现企业价值和获取利润的出路；

B.销售是企业与顾客沟通和联系的渠道；

C.销售是企业营销活动之一；

D.销售是增强企业市场竞争力的主要体现
查看答案