题目

一个带电粒子从A点射入水平方向的匀强电场中,粒子沿直线AB运动,AB与电场线的夹角为30°,如图3-1-14所示.已知带电粒子的质量m=1.0×10-7 kg,电荷量q=1.0×10-10 C,A、B相距L=20 cm.(取g=10 m/s2,结果保留两位有效数字) 图3-1-14(1)试说明粒子在电场中运动的性质,要求说明理由;(2)求电场强度的大小、方向;(3)要使粒子从A点运动到B点,粒子进入电场的最小速度为多大?阅读理解。      Childhood is a happy time, right? Not necessarily. Consider these facts.      Depression may occur in as many as 1 in 33 children.      Once a child has an episode(一段情节) of depression, he or she has a 50 percent chance of experiencing another episode in the next 5 years.      Suicide(自杀) is the 6th leading cause of death for 5-to-15-year-olds.      If your child experiences 5 or more of these signs or symptoms (症状) for at least 2 weeks, he or she may be experiencing depression or another mental illness.      Feeling-Does your child demonstrate: Sadness Emptiness Hopelessness Guilt Worthlessness Lack of enjoyment in everyday pleasures      Thinking-Is your child having trouble: Concentrating Making decisions Completing schoolwork Maintaining grades Maintaining friendships      Physical problems-Does your child complain of: Headaches Stomachaches Lack of energy Sleeping problems ( too much or too little) Weight or appetite changes ( gain or loss )      Suicide risk-Does your child talk or think about: Suicide Death Other morbid (生病的) subjects      Behavior problems-Is your child: Irritable Not wanting to go to school Wanting to be alone most of the time Having difficulty getting along with others Cutting classes or skipping school Dropping out of sports, hobbies or other activities Drinking alcohol or using drugs. Sometimes, a child who causes problems at school or at home may actually be depressed, according to the American Academy of Child and Adolescent Psychiatry. If you think your child may be depressed, it's important to have your child treated. Discuss your child's problems with his or her doctor. The doctor may suggest a referral to a children's psychologist (心理医生) or psychiatrist (精神病医生). Treatment may include individual and family therapy (治疗), along with an antidepressant medication (抗抑郁药). 1. This article is particularly written for ______. A. parents B. teachers C. children D. psychologists 2. Which statement describes a child who may have physical problems? A. The child is always in high mood. B. The child always feels tired but sleeps only four hours a day. C. The child hates to study. D. The child can not concentrate on one thing for a long period. 3. When your child always talks about death or other morbid subjects, he or she ______.  A. may has trouble in thinking B. may have suicide risk C. may have behavior problems D. may have physical problems 4. What should we do when we find our kids experiencing depression? A. Ask for leave to accompany them at home. B. Ask them to take antidepressant immediately. C. Go to see the doctor. D. Ask them to have a good rest.