解物理题时,解有时出现负数、非整数等,这要根据具体的物理过程、物理意义、限制条件等方面进行合理取舍. 1.正负数的取舍 例1 一人在高台阶下某处用较大速度竖直上抛一物体,该物体上升至高台时的速度v0=19.6m／s,问该物体什么时刻经过台下24.5m处? 分析 以高台为坐标原点,以竖直向上的方向为正方向.根据匀变速运动的公式有 When solving a physical problem, the solution sometimes appears negative numbers, non-integers, etc., which are subject to reasonable trade-offs based on specific physical processes, physical meanings, restrictions, etc.. 1. Choice of positive and negative numbers. One used at a high level somewhere. To throw an object at a relatively high speed, the object’s velocity v0 = 19.6m/s when it rises to a high platform, and asks when the object passes through 24.5m below the table. The analysis uses the high table as the coordinate origin, and the vertical direction is upward. For the positive direction, there are equations