It's Sunday morning. There are many people in the park, some boys are playing basketball. There are some girls under a big tree. They're singing and dancing. What are those women doing? They are drinking tea. Look at the woman in a blue coat. Who's she? She's my mother. She is talking to Edward. Edward is her student. He is a good student. He studies hard. He's good at all the subjects. And he's friendly to all his teachers and his friends.

材料二：“面对一千度的烈焰，没有犹豫，没有退缩，用生命助人火海逃生。小巷中带血的脚印，刻下你的无私和无畏，高贵的灵魂浴火涅槃，在人们的心中永生。”这是感动中国节目组给予火海救人英雄王峰的颁奖词。2016年5月18日凌晨，河南省南阳市卧龙区西华村一栋三层居民楼突发大火，在生与死的关键时刻，英雄王锋临危不惧，舍生忘死，挺身而出，以三入火海勇敢救人的实际行动谱写了一曲令人感动的英雄赞歌。

阅读上述材料，运用所学知识，思考下列问题：

一个静止的质点，在两个互成锐角的恒力F₁、F₂作用下开始运动，经过一段时间后撤掉其中的一个力，则质点在撤力前后两个阶段的运动性质分别是（   ）