You (mass 81 kg) and your friend (mass unknown) are in a rowboat(mass 65 kg) on a calm lake. You are at the center of the boatrowing and she is at the back, 2 m from the center. You get tiredand stop rowing. She offers to row and after the boat comes torest, you change places. You notice that after changing places theboat has moved 20 cm relative to a fixed log. What is your friend'smass? (Note that there are two possible solutions. Provideboth.)
