Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Unsure how to begin

  1. Jun 16, 2005 #1
    I'm not even sure how to begin this problem. Can someone help me out?

    A dog, with a mass of 12.0 kg, is standing on a flatboat so that he is 29.7 m from the shore. He walks 8.7m on the boat toward the shore and then stops. The boat has a mass of 44.0kg. Assuming there is no friction between the boat and the water, how far is the dog from the shore now?
  2. jcsd
  3. Jun 16, 2005 #2

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    Think of the boat has having a constant mass/length. Work out the change in center of mass of the dog/boat relative to the center of the boat. What can you say about the position of that center of mass relative to the shore?

  4. Jun 17, 2005 #3
    Imagine that the shore is at the origin of the coordinate system and the dog+boat system lies on the x-axis.Because there is no friction between the boat and water , so there are no external forces.As a fact, in absence of external forces , cente of mass of the system remains stationary .Calculate the x-coordinate of the centre of mass before the dog moves and after the dog moves.Equate both the c.m coordinates and get the needed value.

    X-coordinate of c.m can be calculate as:

    [itex]X_c_m = \frac {m_1 x_1 + m_2 x_2}{m_1+m_2}[/itex]
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook