1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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!

Velocity of fly relative to train tracks

  1. Oct 15, 2007 #1
    1. The problem statement, all variables and given/known data
    A train is moving eastward at 60.0mi/hr. A waiter is walking westward at 2.0mi/hr. A fly is crawling north across the waiter at 3.0mi/hr. What is the velocity of the fly relative to the tracks?

    3. The attempt at a solution
    I don't understand what it means by the fly is crawling ACROSS the waiter. And how I can find out the velocity relative to the tracks.
  2. jcsd
  3. Oct 15, 2007 #2
    Maybe you are having trouble visualizing it. The waiter is on the train and the fly is on the waiter. Imagine the waiter walking around in the train carrying a large plate of food and the fly is crawling across the plate.

    Once you visualize it draw out the vectors and add them up
  4. Oct 15, 2007 #3
    I still don't understand how I would draw it. I draw the 60 mi/hr one, being the train. The head is going to the left. But where is the waiter standing?? Is her tail touching the trains tail??

    Thank you so much.
  5. Oct 15, 2007 #4
    Ok, one way to draw it. You draw the train arrow as you stated. Then you draw the waiter arrow with her tail starting on the head of the train arrow (you will trace back over the train arrow that is ok). Try to draw the arrow sizes relative to one another (the train arrow should be much longer than waiter arrow). Then you draw the bug arrow with the tail starting at the head of the waiter arrow. Then you can make a net (relative) velocity arrow starting from the origin and pointing to the end of the bug arrow. The length of that arrow will the be the relative velocity. You will be able to solve for the length of the net arrow. Remember that the net velocity will have magnitude and direction.
    Last edited: Oct 15, 2007
  6. Oct 15, 2007 #5
    Makes SOOO much more sense.

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook