问题 选择题

已知地球半径为R,地面处的重力加速度为g,一颗距离地面高度为2R的人造地球卫星绕地球做匀速圆周运动,下列说法正确的是 (   )

A.卫星的加速度大小为

B.卫星的角速度为

C.卫星的线速度大小为

D.卫星的周期为

答案

BC

题目分析:根据万有引力提供向心力可知,利用化简则角速度为,B对。线速度为,C正确。加速度应该为,A错。运动周期为,D错。

点评:本题考查了根据万有引力提供向心力的各公式的变形。本题涉及到的公式比较常见,应熟练掌握。

单项选择题
单项选择题

I got a job teaching special education at a school in Coachella, California, a desert town about 170 miles from home. It was no (1) job. Street gangs (2) around the school after dark."Be careful," Dad warned me during one of my frequent weekend (3) home. He was concerned about my living (4) , but I needed to be on my own.One evening, I stayed after school to rearrange my classroom. (5) , I turned out the light and closed the door. Then I (6) toward the gate. It was (7) ! I looked around. Everyone had gone home.After (8) all the exits, I found just enough (9) to squeeze under a gate in the back of the school. Then I walked toward my car, parked in a field behind the building.Suddenly I heard voices. I (10) around and saw at least eight boys following me. (11) my pace, I reached into my shoulder bag to get my key. I (12) all over the inside of my handbag. But the key wasn’t (13) ! Dear Lord, please help me, I prayed (14) . Suddenly, my fingers touched a loose key in my purse. I didn’t even know if it was for my car, but I took it out and (15) it. It worked!I opened the door, slid in and locked it—just (16) the teenagers surrounded the car. Trembling , I started the engine and (17) away. When I returned to my apartment, the phone was ringing. It was my Dad. I didn’t tell him about my experience; I didn’t want to (18) him. "Oh, I forgot to tell you!" He said, "I had a(n) (19) car key made and slipped it into your purse—just (20) you ever need it.

第(14)空应选择()

A.loudly

B.nervously

C.carefully

D.silently