试题与答案

质点做直线运动,选定它的运动方向为正方向,某时刻它的加速度a>0,位移s>0,若

题型:选择题

题目:

质点做直线运动,选定它的运动方向为正方向,某时刻它的加速度a>0,位移s>0,若从这个时刻开始,使质点的加速度逐渐减小,则:(    )

A.质点的速度逐渐减小,直到加速度变为零为止

B.质点的速度一直增大

C.质点的位移继续增大,直到加速度变为零为止

D.质点的位移继续增大,加速度变为零后位移还要继续增大

答案:

答案:D

题目分析:质点的加速度虽然减小,但是加速度方向仍旧和速度方向相同,故质点仍旧做加速运动,只不过在单位时间内的速度增加量在减小,当加速度减小到零的时候,速度达到最大,之后做匀速直线运动,速度方向不变,所以位移仍旧在增大,当加速度为零后,位移仍旧在增大,所以D正确,

点评:加速度表示物体速度变化快慢的物理量,当加速度和速度方向同向时,做加速运动,当加速度方向和速度方向反向时,做减速运动,

试题推荐
题型:单项选择题

In ancient Greek, the term euthanatos meant "easy death". Today euthanasia (安乐死) generally refers to mercy killing, the voluntary (自愿) ending of the life of someone who is terminally ill. Like abortion, euthanasia has become a legal, medical, and moral issue over which opinion is divided.

Euthanasia can be either active or passive. Active euthanasia means that a physician or other medical personnel takes an action that will result in death, such as giving an overdose of deadly medicine. Passive euthanasia means letting a patient die for lack of treatment, or stopping the treatment that has begun. Examples of passive euthanasia include taking patients off a breathing machine or removing other life-support systems. Stopping the food supply is also considered passive.

A good deal of the debate about mercy killing originates from the decision-making process. Who decides whether a patient is to die This issue has not been solved legally in the United States. The matter is left to state law, which usually allows the physician in charge to suggest the option of death to a patient’s relatives, especially if the patient is brain dead. In an attempt to make decisions about when their own lives should end, several terminally ill patients in the early 1990s used a controversial suicide device, developed by Dr. Jack Kevorkian, to end their lives.In parts of Europe, the decision-making process has become very flexible. Even in cases where the patients are not brain dead, patients have been put to death without their approval at the request of relatives or at the suggestion of physicians. Many cases of passive euthanasia involve old people or newborn infants. The principle justifying this practice is that such individuals have a "life not worthy of life".In countries where passive euthanasia is not legal, the court systems have proved very tolerant in dealing with medical personnel who practice it. In Japan, for example, if physicians follow certain guidelines they may actively carry out mercy killings on hopelessly ill people. Courts have also been somewhat tolerant of friends or relatives who have assisted terminally ill patients to die.

The principle justifying passive euthanasia in Europe is that terminally ill patients are ().

A. living a life without consciousness

B. living a life that can hardly be called life

C. too old or too weak to live on

D. too old or too young to approve of euthanasia

查看答案
微信公众账号搜索答案