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!

Walking on a boat

  1. Jul 21, 2014 #1
    hi all, here's the problem
    "A dog sits on the left end of a boat of length L that is initially adjacent to a dock to its right. The dog then runs toward the dock, but stops at the end of the boat. If the boat is H times heavier than the dog, how close does the dog get to the dock?

    Ignore any drag force from the water. "

    So, on the internet I found the answer that it's L/(1+H) but it didn't provide any explanation

    could someone help me understand how to approach problems like this. Basically I'm really stuck on problems like " walking on a block on a friction less surface " . So I know it's got something to do with the fact that the Center of Mass doesn't change position, only the block ( boat in that case ) and the object moving( dog). Could someone help me out with this ? thank you so much if you do :)
     
  2. jcsd
  3. Jul 21, 2014 #2

    jbriggs444

    User Avatar
    Science Advisor

    If the dog moves 1 unit distance to the right, the boat beneath his feet must move 1/H unit distance to the left to keep the center of gravity at the same place. The net movement of the dog relative to the boat is 1+1/H. The net movement of the boat relative to the water is 1/H.

    Express this ratio as boat movement (relative to dock) divided by dog movement (relative to boat)

    [itex]\frac {\frac {1} {H}}{1 + \frac {1}{H}} [/itex] = [itex]\frac {\frac {1} {H} }{\frac{H}{H} + \frac {1}{H}}[/itex] = [itex]\frac {\frac {1} {H} }{\frac{H + 1}{H}} [/itex] = [itex]\frac{1}{H+1}[/itex]

    If the dog moves distance L from the left end of the boat to the right, how far does the right end of the boat move away from the dock?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Walking on a boat
  1. Walked or played (Replies: 5)

  2. Walking on Wagon (Replies: 2)

  3. Friction for walking (Replies: 25)

Loading...