The displacement of an object from the top of the inclined plane to the bottom of the inclined plane is S1 in the first three seconds and S2 in the last three seconds It is known that S1 + S2 = 1.2m, Si: S2 = 3:7 In one step, I can't figure out why v = V 0 + at = 0.28 + 0.08 * 1.5, that 1.5 is. Isn't V 0 the initial velocity? Why can we use the average velocity instead Calculate S1, S2, then a = 0.08, then calculate the average speed in the next 3 seconds = 0.28, then calculate the final speed, calculate t according to v = at, and then substitute t into S = 1 / 2at ˇ 2 to calculate s = 1m, but when calculating the final speed, it is how to calculate v = V0 + at = 0.28 + 0.08 * 1.5, and 0.28 is how to substitute the average speed into the initial speed

The displacement of an object from the top of the inclined plane to the bottom of the inclined plane is S1 in the first three seconds and S2 in the last three seconds It is known that S1 + S2 = 1.2m, Si: S2 = 3:7 In one step, I can't figure out why v = V 0 + at = 0.28 + 0.08 * 1.5, that 1.5 is. Isn't V 0 the initial velocity? Why can we use the average velocity instead Calculate S1, S2, then a = 0.08, then calculate the average speed in the next 3 seconds = 0.28, then calculate the final speed, calculate t according to v = at, and then substitute t into S = 1 / 2at ˇ 2 to calculate s = 1m, but when calculating the final speed, it is how to calculate v = V0 + at = 0.28 + 0.08 * 1.5, and 0.28 is how to substitute the average speed into the initial speed

My approach: it's not the same as your answer
Your habit is very good. V0 is the initial speed, but it can also express a certain speed in the whole process. You just learned this. Just practice more,