A 56-kg woman contestant on a reality television show is at rest at the south end of a horizontal 147-kg raft that is floating in crocodile-infested waters. She and the raft are initially at rest. She needs to jump from the raft to a platform that is several meters off the north end of the raft. She takes a running start. When she reaches the north end of the raft she is running at 4.6 m/s relative to the raft. At that instant, what is her velocity relative to the water?
Psystem = Pwoman + Praft = 0
Pwoman(f) - Pwoman(i) + Praft(f) - Praft(i) = 0
The Attempt at a Solution
I've split up the momentums into their each individual parts. The mass of the woman is 56kg, the raft is 147kg, and this is where I'm stuck. I believe that Pwoman(i) and Praft(i) are 0 because they both are initially at rest. Now I have Pwoman(f) + Praft(f) = 0. I don't know where to plug in her speed (Pwoman or Praft?), and either way, I would get a negative answer. Can someone help me figure out where to go from here?