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!

What did I do wrong? (Newton's Second Law)

  1. Nov 7, 2005 #1
    Only two horizontal forces act on a 3.0 kg body. One force is 9.0N, acting due east, and the othr is 8N, acting 62 degrees north of west. What is the magnitude of the body's acceleration?
    Fnet= ma ............so I took that to mean F1x + F2x = ma
    F1x = 9 cos 0 = 9
    f2x = 8 cos 62 = 3.76
    a = (9 + 3.76)/3 = 4.25
    The solution says 2.9
     
  2. jcsd
  3. Nov 7, 2005 #2

    arildno

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    East and west are opposite directions. What does that tell you?
     
  4. Nov 7, 2005 #3
    I think it tells me that it should be F1 - F2 instead. If yes then

    a = (9 - 3.76)/3 = 1.75

    It still doesn't come to 2.9
     
  5. Nov 7, 2005 #4

    arildno

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    Oops, sorry to mislead you a bit.
    The MAGNITUDE of the acceleration evidently includes the contribution from the VERTICAL acceleration the body also expriences.
    That is, you are to find [itex]a=\sqrt{a_{x}^{2}+a_{y}^{2}}[/itex]
     
  6. Nov 7, 2005 #5
    You're right because I got the answer using it, but I don't know why. The problem says that only 2 'horizontal' forces act on the object. Why is the vertical involved? I know F2 is making an angle, but then what do they mean by horizontal forces? Shouldn't it just say 'forces'? I have a sample problem in the book that specifies there is one-dimensional motion yet 1 of the forces is making an angle.
     
  7. Nov 7, 2005 #6

    arildno

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    The phrasing in the book is just dumb, that's all there is to it.
     
  8. Nov 7, 2005 #7
    thanks for your help
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: What did I do wrong? (Newton's Second Law)
  1. What did i do wrong? (Replies: 3)

  2. What did I do Wrong ? (Replies: 10)

  3. What did I do wrong? (Replies: 4)

  4. What did I do wrong? (Replies: 6)

Loading...