Posted by Priyanka on Sunday, March 18, 2012 at 4:02am.
A 44.0kg woman stands at one end of a 148 kg raft that is 6 m long. The other end of the raft is 0.5 m from a pier.
(a) The woman walks toward the pier until she gets to the other end of the raft and stops there. Now what is the distance between the raft and the pier? in m please
(b) How far did the woman walk (relative to the pier)? in m please
I tried the following:
(44*5)+(148*0.5)/(44+148) but i get the wrong answer I don't know what I am doing wrong! And for b I don't know how to do that! Please help am confused! Thank you.

Physics  drwls, Sunday, March 18, 2012 at 9:11am
They want you to neglect friction between the boat and the water. With that assumption, the center of mass of the boat and woman remain in the same place, relative to the pier. When she stops walking, the boat stops moving.
Let X be the distance of the close end of the boat from the pier. Initially
X = Xi = 0.5 m. Afterwards, X = Xf. You want to know the value of Xf.
Initial CM location =
[148*3.5 + 44*6.5]/(148+44) = 4.188 m
Final CM location =
[148*(3+Xf) + 44*Xf]/192 = 4.188
Solve for Xf
804= 444 + 148 Xf + 44 Xf
360 = 192 Xf
Xf = 1.875 m
The boat ends up farther from the pier, although the woman ends up closer to it.
(b) The woman was initially 6.5 m from the pier and ended up 1.875 m away. She moved 4.625 m closer, relative to the pier.

Physics  Priyanka, Sunday, March 18, 2012 at 12:57pm
Thank you Drwls! I really appreciate your help.
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