一打点计时器固定在斜面上某处，一小车拖着穿过打点计时器的纸带从斜面上滑下，如图a所示，图b是打出的纸带的一段。

（1）已知打点计时器使用的交流电频率为50Hz，利用图b给出的数据可求出小车下滑的加速度a=______________。

（2）为了求出小车在下滑过程中所受的阻力，还需测量的物理量有_________________，用测得的物理量及加速度a表示阻力的计算式为=_____________________。

用所给单词的适当形式填空。

1. You are in poor health and you must give up _____. (smoke)

2. You should do more _____ (exercise). Don't always sit at the desk busy doing your _____. (exercise)

3. We all love Miss Yang. She always makes her history class very_____. (interest)

4. Foreign stamps _____ him. (interest)

5. Her parents wouldn't allow her to marry anyone _____ family was poor.(who)

6. When their car becomes old, they prefer_____ (buy) a new one rather than _____ (repair) it.

7. I prefer _____ (do) exercise to _____ (watch) TV.

8. His mother refused _____ (buy) him a present.

9. He is sure to come. I've_____ (persuade) him to attend our meeting.

10. I tried to persuade him _____ (give) up _____ (smoke), but failed.