搜题请搜索小程序“爱下问搜题”
问题 选择题

重600N的物体放在水平地面上，与水平地面间的最大静摩擦因数为0.3，动摩擦因数为0.2，当用150N的水平推力时，物体受到的摩擦力（　　）

A．60N

B．120N

C．150N

D．180N

答案

物体对地面的压力大小FN=G=600N，物体与地面间的最大静摩擦力Fm=μ静FN=0.3×600N=180N

水平拉力F=150N＜Fm，说明物体没被拉动，仍处于静止状态，则由平衡条件得

物体受到的摩擦力f=F=150N

故选C

单项选择题

Expressing gratitude is an important form of good manners. Nowadays more and more people in China have found it’s high time to (1) a thankful heart for the young.Everyone likes to get praised and appreciated. Gratitude is the greatest of virtues, which lets others smile and makes the world more beautiful. You just need several minutes to write down a thank-you note, but it brings much joy to the (2) .We live in a society where we enjoy the different services of others. But (3) of them should be taken for granted.Gratitude is also a kind of (4) in life. In developing gratitude for every moment—for the simple joys and even for the (5) times—we come to truly enjoy and appreciate life. Then we are able to see the (6) that surrounds us.Try to write a thank-you letter to your parents for working hard to (7) you a happy life.Be grateful to your teachers because of their (8) with your studies and character building.Say thanks to your friends who (9) both your happiness and sorrow. We are sure it will bring them much joy and add (10) into your own life as well.

第（8）空应选择（）

A．study

B．part

C．help

D．cooperation
查看答案
填空题

图CD段中，水的内能________。请你计算在CD段中水所吸收的热量              。在用酒精灯给水加热的过程中，若酒精灯的热效率为40%，则请你计算酒精灯放出的热量是              。

查看答案