A classmate used stroboscopic photography to take a photo of "a small ball doing a flat toss" as shown in the picture.

The ball is shot every 0.5 seconds. The initial speed of the ball in the horizontal direction is 10cm/s, and the initial speed of free fall is 2.5cm/s.

Suppose the initial velocity in the vertical direction when taking the first picture is v0, v0t+1/2gt^2=2.5 (Equation 1); when taking the second picture, the initial velocity in the vertical direction is v1, v1t+1 /2gt^2=5 (Equation 2); Subtract Equation 1 from Equation 2 to get v1t-v0t=2.5, and because v1=vgt, substitution can be solved to get t=0.5, and this problem is solved.