2015年泛珠三角及中华名校物理奥林匹克邀请赛试题及答案.pdf

2015 年泛珠三角及中华名校物理奥林匹克邀请赛 Pan Pearl River Delta Physics Olympiad 2015 Pan Pearl River Delta Physics Olympiad 2015 2015 年泛珠三角及中华名校物理奥林匹克邀请赛 Sponsored by Institute for Advanced Study, HKUST 香港科技大学高等研究院赞助 Part-1 (Total 5 Problems) 卷-1 （共5题） (9:00 am – 12:00 pm, 25 February, 2015) Numerical answers should be given to 3 significant figures.数字答案请给三位有效数字。 1. Retrograde Motion of Mars (9 points) 火星的逆行运动 （9 分） In the history of astronomy, the phenomenon of the retrograde motion played an important role. Suppose we observe the position of Mars at midnight every night for many nights. Using distant stars and constellations as the background, we will find that Mars moves from West to East most of the time. However, there are periods of time that Mars is observed to move in opposite direction, as shown in the figure. The orbital period of Mars is 1.88 y. Assume that the orbits of Earth and Mars are circular, and the tilting of Earth’s axis can be ignored. 在天文史上，行星的逆行运动扮演了重要的角色。假设我们连续多个晚上在午夜观察火星的位置。 若以远处的星体和星座为背景，我们会发现大部分时间火星是从西到东运动，但也有些时段是逆 向运动，如图所示。火星的轨道周期是 1.88 年。假设地球和火星的轨道都是圆的，地轴的倾斜可 略。 Distant constellation 远处的星座 Star T t = 0 星T t 0 West t 0 西 East 东 o o o o o o o o 20 15 10 5