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．