题目

关于物体做曲线运动的条件，下述说法正确的是（    ）A.物体一定要在恒力作用下运动B.物体一定要在变力作用下运动C.只要合力的方向变化，物体一定会做曲线运动D.做曲线运动的物体所受的合力方向一定是变化的 答案：解析：物体受恒力作用时，恒力的方向只要与速度方向不在一条直线上，物体就能够做曲线运动.物体在变力作用下会有两种可能，一种是力的大小变化，而方向并不发生变化的物体可能做曲线运动，也可能做直线运动.物体的受力方向与速度方向总在一条直线上，物体做变加速直线运动，满足力的方向The island Fiji has always been around me in my life. My parents met in Fiji when my father was a teacher as a Peace Corps volunteer and my mother a student. They taught me about its people, culture, foods and religious beliefs. At the age of two, I made my first trip across the Pacific Ocean to Fiji. My mother and I made that trip unexpectedly because my grandma was ill and longed to see her American granddaughter. Although I have few memories of that first trip, I do remember grandma braiding (编辫子)my hair every day. The brush gliding through my hair is a feeling I will treasure forever because she passed away soon. I returned to America when I was five years old. This time I had a brother, Martin, who was two. I resisted my third trip to Fiji when I was 15, being a teenager who did not want to spend the summer away from friends. It was this trip, however, that made me realize that Fiji is not just a place to visit but a part of who I am. The smells and sounds and sights came back to me, but the best part was getting to know my relatives. Vishal was one cousin I quickly bonded with. Born two days before me, I had only known him through pictures before. Though raised oceans apart in different cultures, we talked and laughed about everything from American sports to Fijian dancing. I was able to form close ties with all my cousins, and when I talk about them now, it’s as if I have known them my whole life. Spending time with them helped me understand the traditions and values my mother grew up with. Hospitality and care and respect for family members are central values in Fijian culture. I truly enjoyed learning about my roots during this trip. Fiji is just like a second home, and I will never forget the time I have spent there1.From the passage, we can learn that ______.A.the author’s parents had been classmates beforeB.the author had lived in Fiji for about five yearsC.the author had no memories of her grandmaD.people value family in Fijian culture2.The author resisted her third trip to Fiji because ______.A.she didn’t want to separate from her brotherB.she didn’t know her cousins there very wellC.she didn’t want to separate from her American friendsD.her grandma had passed away3.Which of the following is TRUE about Vishal?A.He is younger than the authorB.The author had met him on her first trip to FijiC.He and the author had lots of common interestsD.He and the author held different opinions about Fijian culture