A92-kg rugby player running at 7.5 m/s collides in midair with a 112-kg player moving in the opposite direction. after the collision each player has zero velocity.

what was the initial speed of the 112-kg player before the collision?

Dust and gases contract.

Repeated trials allow you to calculate a mean which can reduce the effect of random errors to make your results more precise.your results will also be reproducible therefore if someone else did the same experiment they'd get the same results which would make your results more reliable.