1. The problem statement, all variables and given/known data A glider of length moves through a stationary photogate on an air track. A photogate shown in the figure below is a device that measures the time interval Δtd during which the glider blocks a beam of infrared light passing across the photogate. The ratio vd = /Δtd is the average velocity of the glider over this part of its motion. Suppose the glider moves with constant acceleration. (a) Argue for or against the idea that vd is equal to the instantaneous velocity of the glider when it is halfway through the photogate in space. (b) Argue for or against the idea that vd is equal to the instantaneous velocity of the glider when it is halfway through the photogate in time. 2. Relevant equations None 3. The attempt at a solution On (a), I'm not exactly sure how to think of this problem. What does it mean by space? Regarding (B), I believe the instantaneous velocity is equal to the average velocity at the halfway point. This is because the velocity decreases linearly.