1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Center of mass question

  1. Nov 11, 2006 #1
    this question has really stumped me.

    23 people on a boat rest on water without friction. Each person has an average mass of 70 kg, and the boat itself weighs 10^4 kg. The entire party walks the entire 8 m distance of the boat from bow to stern. How far (in meters) does the boat move?

    i know i have to use this equation somwhere:

    x_cm = ( m1x1 + m2x2 ) / ( m1 + m2 )

    so far i think
    m1 = 23 * 70
    x1 = 0
    m2 = ?
    x2 = ?

    can anyone help me?

    thnx
     
    Last edited: Nov 12, 2006
  2. jcsd
  3. Nov 12, 2006 #2
    You have data to calculate the center of mass before the people move. Since, there are no external forces acting on the c.m., will he change?

    So,

    [tex]x_{cm}_{i} = x_{cm}_{f}[/tex]​
     
  4. Nov 12, 2006 #3
    is it like this?

    in an isolated system, momentum is conserved. so, m1v1=m2v2, were m1 is the mass of boat, v1 is it's velocity, m2 is the mass of all the people, v2 is the velocity of them,

    v2=(m1v1)/m2
    d2/t=m1/m2 x d1/t
    d2=m1/m2 x d1

    since every1 covers d1, assume that the center of mass is over 1point that covers the 8meters....

    does this make sense?
     
  5. Nov 12, 2006 #4
    no i dont think im makes sense cuz we're not dealing with velocity here
     
  6. Nov 12, 2006 #5
    so i got this so far but i dunno which is which to plug in

    [tex]m_{1}x_{1}_{i} + m_{2}x_{2}_{i} = m_{1}x_{1}_{f} + m{2}x_{2}_{f}[/tex]​

    am i on the right track?
     
    Last edited: Nov 12, 2006
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Center of mass question
Loading...