You see how long you are in the air and the whole time you are in the air, you are traveling horizontally at this speed.

你可以知道在空中停留的时间,当你在空中运动的时候,你一直以这个水平速度在运动

耶鲁公开课 - 基础物理课程节选

This says, if you want to be in the air for a long time, so you may think that 90 degrees is the best angle.

也就是说,如果你想在空中停留更久,你也许会认为 90°是最佳选择

耶鲁公开课 - 基础物理课程节选