1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Forces - Finding Net Force

  1. Sep 30, 2007 #1
    1. A ball is flying through the air, and at a given point in the flight, the ball is submitted to a gravitational force: F(g) = 1,5 N [downwards] and air resistance: F(air) = 0,50 N [32° above the horizontal]. Calculate the net force on the ball.

    2. F (nette) = m x a

    3. I thought I might have to find the vertical and horizontal components of the air resistance, so I found:
    sin32 x 0,5N = 0,26N = x
    cos32 x 0,5N = 0,42N = y

    I also tried calculating the mass of the ball, in case it might prove useful:
    Fg = m x g
    1,5N = 9,8m
    0,153 kg = m

    But after calculating these values, I'm at a loss of what to do next. How do you find out the net force without having the other force on the horizontal axis? How can I use this data to calculate the net force? The answer key in my book says it should be 1,3N [71° under the horizontal], but I have no idea how this answer was achieved. I would be grateful for any help in solving this problem.
  2. jcsd
  3. Sep 30, 2007 #2
    You have the x and y components interchanged.

    Why should it have a non-zero horizontal component?

    Think of it this way: "Downwards" is 270 degrees away from the positive x-axis. Can you find the components of the gravitational force now?
  4. Sep 30, 2007 #3
    If the ball is in movement, shouldn't the horixontal component be non-zero?

    And what does it being 270 degrees away from the positive x-axis have to do with it?
  5. Sep 30, 2007 #4
    To find the net force just add the two force vectors. You know what their components are along each direction.

    I was just trying to show you that the horizontal component of the gravitational force is zero.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook