If you're taking two derivatives you can add a constant and something linear in t.

如果你要二次求导,你可以添加一个一次项和常数项

耶鲁公开课 - 基础物理课程节选

If you're taking only one derivative you can add a constant.

如果只进行一次求导,你可以添加一个常数项

耶鲁公开课 - 基础物理课程节选