题目

It's the third time late this month. A . that you arrived B . when you arrived C . that you have arrived D . when you have arrived 答案：C2．小华参加体育中考的跳绳考试时，她在1min内连续跳了150次，获得跳绳项目的满分．已知小华的质量为45kg，每只鞋底与地面的接触面积为150cm2时，跳起时重心升高的平均高度为4cm．g取10N/kg．求：（1）小华跳一次所做的功；（2）小华跳绳时的平均功率．