蓄电池充电是电能变成化学能,蓄电池放电是化学能变成电能()
参考答案:对
阅读理解。
Jane Black is from Canada. She is twelve years old. Now she is a junior high school (初中) student in
Ningde. She is in Class 8, Grade 7. Her telephone number is 283-6698. Hu Hua is Chinese. His English name
is Tom White. He is in Class 3, Grade 7. His cellphone (移动电话) number is 892-4148. Jane and Hu Hua are
in different (不同的) classes, but they are good friends.
1. Jane is from _______.
A. England
B. Japan
C. Canada
2. Jane is _______.
A. eleven
B. twelve
C. thirteen
3. She is in Class _______, Grade _______.
A. Eight; Seven
B. eight; seven
C. Seven; Eight
4. Hu Hua's cellphone number is _______.
A. 283-6698
B. 892-4148
C. 669-8481
5. Are Jane and Hu Hua in the same class?
A. No, they aren't.
B. Yes, they are.
C. We don't know.
如图所示,质量为M的铁箱内装有质量为m的货物.以某一初速度向上竖直抛出,上升的最大高度为H,下落过程的加速度大小为a,重力加速度为g,铁箱运动过程受到的空气阻力大小不变.求:
(1)铁箱下落过程经历的时间;
(2)铁箱和货物在落地前的运动过程中克服空气阻力做的功;
(3)上升过程货物受到铁箱的作用力.