How Far Does the Boat Move When Juliet Joins Romeo at the Rear?

[Chuck 86]

Homework Statement

Romeo (80.3 kg) entertains Juliet (58.0 kg) by playing his guitar from the rear of their boat at rest in still water, 2.73 m away from Juliet who is in the front of the boat. After the serenade, Juliet carefully moves to the rear of the boat (away from shore) to plant a kiss on Romeo's cheek. How far does the 80.5 kg boat move toward the shore it is facing?

Homework Equations

Xcm=m1x1+m2x2+m3x3
m1+m2+m3

The Attempt at a Solution

i don't really know what I am doing on this problem because the professor didnt explain very well...at all

 

[tiny-tim]

Hi Chuck 86!

There are no (horizontal) external forces on the boat-and-Romeo-and-Juliet, so its centre of mass will stay in the same place!