补充说明，图中Oa竖直相距一格，ab竖直相距2格。讲解该问题---**Extraction Content:**
1. (多选) 某同学通过频闪照相的方法研究平抛物体的运动，用一张印有小方格的纸记录小球在平抛运动途中的几个位置。得到实验如图所示，图中背景方格坐标每一个边长为 $l=10\text{cm}$。一物体做平抛运动时分别经过$O$、$a$、$b$三点，取重力加速度$g=10\text{m/s}^2$，则下列结论中正确的是（ ）
A. 速度的变化量$\Delta v_{aO} = \Delta v_{ba}$
B. 小球的抛出速度$v=1\text{m/s}$
C. $a$点的速度$v_a=2.5\text{m/s}$
D. 小球抛出点的坐标为$(-5\text{cm}, -1.25\text{cm})$（以$O$点为坐标原点，向下为$y$轴正方向，小球水平方向为$x$轴正方向）
写出各选项求解过程：
**Chart/Diagram Description:**
* **Type:** Grid with labeled points.
* **Main Elements:**
* A grid of squares is shown.
* Three points are marked on the grid, labeled O, a, and b.
* Point O is located at the intersection of grid lines, approximately two squares from the left edge and one square from the top edge of the visible grid.
* Point a is located two squares to the right and one square down from point O.
* Point b is located two squares to the right and three squares down from point a (or four squares to the right and four squares down from point O).
* The labels 'O', 'a', and 'b' are placed near their corresponding points.
* The problem statement indicates the side length of each grid square is $l = 10\text{cm}$.