A 45kg boy is holding a 12kg pumpkin while standing on ice skates on a smooth frozen pond. The boy tosses the pumpkin with a horizontal speed of 2.8m/s to a 37kg girl (also wearing ice skates) catches it. What are the final speeds of the boy and girl?
For the boy holding the pumpkin, initial momentum is 0. After tossing it, he will have momentum equal and opposite that of the pumpkin:
For the girl, after catching the pumpkin she will have all the momentum the pumpkin had in flight:
Notice that both their momenta total to zero: