问题 选择题

某人骑着自行车向前匀速行使时,关于自行车前、后轮所受的摩擦力方向,下列说法中正确的是:   

A.都向前

B.都向后

C.前轮向后,后轮向前

D.前轮向前,后轮向后

答案

答案:C

分析:静摩擦力方向与物体间相对运动趋势的方向相反.人骑着自行车向前匀速行使时,前后轮均受地面的静摩擦力作用,根据车轮相对于地面的运动趋势方向,判断摩擦力方向.

解答:解:人骑着自行车向前匀速行使时,后轮相当于主动轮,后轮与地面接触点地面的运动趋势方向向后,则地面对后轮的静摩擦力方向向前.前轮相当于从动轮,前轮与地面接触点地面的运动趋势方向向前,则地面对前轮的静摩擦力方向向后.

故选C

填空题
阅读理解

阅读理解

     Since we are social beings, the quality of our lives depends in large measure on our interpersonal

relationships. One strength of the human conditions is our possibility to give and receive support from

one another under stressful conditions. Social support makes up of the exchange of resources among

people based on their interpersonal ties. Those of us with strong support systems appear better able to

deal with major life changes and daily problems. People with strong social ties live longer and have better

health than those without such ties. Studies over types of illnesses, from depression to heartdisease, show

that the presence of social support helps people defend themselves against illness, and the absence of

such support makes poor health more likely.

     Social support cushions stress in a number of ways. First, friends, relatives and coworkers may let us

know that they value us. Our selfrespect is strengthened when we feel accepted by others in spite of our

faults and difficulties. Second, otherpeople often provide us with informational support. They help us to

define and understand our problems and find solutions to them. Third, we typically find social

companionship supportive. Taking part in freetime activities with others helps us to meet our social

needs while at the same time distracting(转移注意力)us from our worries and troubles. Finally, other

people may give us instrumental support-money aid, material resources, and needed services-that

reduces stress by helping us resolve and deal with our problems.

1. Interpersonal relationships are important because they can________.

A. make people live more easily

B. smooth away daily problems

C. deal with life changes

D. cure types of illnesses

2. The researches show that people's physical and mental health________.

A. lies in the social medical care systems which support them

B. has much to do with the amount of support they get from others

C. depends on their ability to deal with daily worries and troubles

D. is related to their courage for dealing with major life changes

3. Which of the following is closest in meaning to the underlined word "cushions"?

A. takes place of  

B. makes up of

C. lessens the effect of  

D. gets rid of