Compute each part of given question:
Question: A tennis ball gun launches tennis balls at 19.9m/s. It's pointed straight up and launches one ball; 2.0 s later, it launches a second ball.
Part I: At what time (after the first launch) are the two balls at the same height?
Part II: What is that height?
Part III: What is the first balls' velocity at that point?
Part IV: What is the second balls' velocity at that point?
Write your solution in appropriate format and provide references for above question thanks.