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: Kite string force, negative or positive>

  1. Jan 24, 2009 #1
    1. The problem statement, all variables and given/known data

    A kite string exerts a 12-lb pull (|F|) on a kite and makes a 45 degree angle with the horizontal. Find the horizontal and vertical components of F.

    2. Relevant equations

    Pythagorean

    3. The attempt at a solution

    12*sqrt(2) for both horizontal and negative

    My question is whether to assign a positive or negative to either value? It seems that either could work with the limited assumptions in the question? Or would it be more appropriate for the y force to be negative?
     
  2. jcsd
  3. Jan 24, 2009 #2
    Hi 2clients, well actually this really does depend. When you have a taught string, as we have in your question, there is a tension in the string. Now this tension can be model as acting in both direction along the string. Imagine for example you help a piece of sting in your hands and pulled both ends, there is a force stopping both hands move further apart when the string is taught, so there must be a force acting on you right had to the left, and you left hand to the right :D

    So what you need to ask is in which direction do you want the tension to be acting for the purpose of you question. In the question its says it exerts a pull on the kite, so the tension will be acting down the sting towards the person holding the sting, acting away from the kite, so it will have a negative y value and and may have a negative or positive x value depending on where the person is standing relative to the kite :D

    That all said, most question wouldn't ask you to work out negatives and posatives, and they will simply want to know the magnitude of a force or the magnitude of its components, which are always positive :-) hope that helped

    ps sorry if you knew most of that already, obviously I don't know what you already know :D
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook