This Question is a multi-parter but all around the same scenario. Similar to an end of paper A-level physics question.

Alex and Billy are launching the air rockets they made by launching them using a bike pump. They each have a rocket, a launchpad, a bikepump connected to it and their teacher Daniel has two stopwatches. They both press down on the bike pump as hard as they can at exactly the same time and this blast of air pushes the rocket upwards. Daniel starts the stop watch exactly as they leave the launchpad on the ground. Daniel will stop the stopwatch for each rocket when it falls back down and hits the ground.