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!

Investigating Newtons law

  1. Mar 31, 2016 #1
    1. The problem statement, all variables and given/known data
    upload_2016-3-31_19-42-17.png


    2. Relevant equations
    no equations required

    3. The attempt at a solution
    i already answered the question, but i just want to know if i wrote the right direction for the Fnet.
    is it [N 10 W] or [W 10 N]?

    upload_2016-3-31_19-43-21.png

    this is how i wrote it:
    Fnet: 1165 N [N 10 degrees W]

     
  2. jcsd
  3. Mar 31, 2016 #2

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    As I explained in another thread, N 10 degrees W would mean 10 degrees W of North. Is that what it looks like in your diagram?
    Also, you don't show how you got 10 degrees. It is correct, to that many digits. Can you quote one more digit?
     
  4. Mar 31, 2016 #3
    ok this is how i got 10 degrees and the Fnet:

    Step #1: Use the cosine law to solve for the magnitude of the net force


    c2 = a2 + b2 – 2abcosC

    c2 = (800 N)2 + (400 N)2 – 2(800 N)(400 N)cos150 degrees

    c = 1165 N


    Step #2: Use the sine law to solve for the angle of the net force

    SinB/b = SinC/c

    SinB/400 N = Sin150 degrees/1165 N

    b = sin-1 (400 N x Sin150o/1165 N)

    b = 9.8 » 10 degrees

    To determine the angle for the net force, subtract 20 fromb, as this results in the angle needed to describe the direction of the net force.

    20 degrees – 10 degrees = 10 degrees

    Fnet = 1165 N [N 10 degrees W] it can also be looked at as 10.2 degrees, i just rounded 9.8 to 10 exactly.

    The net force on the log is 1165 N at an angle of 10 degrees west of north.
     
  5. Mar 31, 2016 #4
    in this case, the 800 N vector is further to the north and the resultant (Fnet) is further to the west.
    i described the angle between them by saying [N .... W]
    upload_2016-3-31_22-26-53.png
    so is this correct?
     
  6. Mar 31, 2016 #5

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Yes, that's fine.
    This is the identical mistake you are making on the other thread. When stating the direction of the resultant, we no longer care about any of the directions of the contributing forces. We must quote the direction relative to the standard compass points.
     
  7. Mar 31, 2016 #6
    upload_2016-3-31_23-9-34.png
    upload_2016-3-31_23-9-10.png
    ok so in this example taken from my lesson, the 1.0 N vector is directed East, and the Fnet is further north, to describe the direction, they said the Fnet was E....N
    can't this method be applied to my problem as well?
     
  8. Mar 31, 2016 #7
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: Investigating Newtons law
  1. Newton's Law (Replies: 2)

  2. Newtons law (Replies: 5)

  3. Newton's laws (Replies: 78)

  4. Newton's Laws (Replies: 3)

  5. Newton's Law (Replies: 3)

Loading...