A glider of length , moves through a stationary photogate on an air track. A photogate (Fig. P2.39) is a device that measures the time interval ∆td during which the glider blocks a beam of infrared light passing across the photogate. The ratio vd = l/∆td 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.