It's useful to have the average acceleration, which you can find by taking similar differences of velocities.

平均加速度也是很有用的,你可以用类似方法,取速度的变化量求出来

耶鲁公开课 - 基础物理课程节选

So, that is a tricky problem to begin with because if you take this formula here, it tells you y if you know t, but no, we're not saying that.

以这个问题刚开始的时候有点难度,因为如果你要用这个公式,求y的时候就一定要知道t,但是,我们不知道

耶鲁公开课 - 基础物理课程节选