You are sitting in a wagon and rolling horizontally at 5 m/s when your little sister jumps into your lap as you pass by. Your mass is 50 kg, your sister's mass is 20 kg, and that of the wagon is 3 kg.
a) Does this situation represent an elastic or an inelastic collision? Explain your reasoning.
b) What physical quantities are conserved in this kind of collision?
c) Calculate the speed of the wagon after your little sister jumps in.