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Homework Help: Force on projected object at its highest point. What is the net force?

  1. Sep 20, 2009 #1
    1. The problem statement, all variables and given/known data
    A ball with a weight of 1.0 N is thrown at an angle of 30 degrees above the horizontal with an initial speed of 12 m/s. There is no air resistance acting on the ball. At its highest point, the net force on the ball is:
    A. 4.9 N, 30 degrees below horizontal
    B. zero
    C. 4.9 N up
    D. 4.9 N down
    E. None of the above

    2. Relevant equations
    Fnet= ma

    3. The attempt at a solution

    I am guessing that since there is no wind resistance, there is no acceleration in the X direction. Thus, the horizontal force is zero.

    The force in the y direction should remain constant because gravity is a constant (9.8 m/s^2) and the mass is a constant. Thus, I am thinking that the net force should equal 1N.
    My answer would be E. None of the above. I always get paranoid about choosing none of the above as my answer. Could someone please confirm that this is the proper way of going about this question?

    Thank you so much!
  2. jcsd
  3. Sep 20, 2009 #2
    I would say your reasoning is spot on.

    I hope I did not break any forum rules,
    if so, I apologize.
  4. Sep 20, 2009 #3


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    Homework Helper

    Yup, it's 1 N. Gravity is the only force that can possibly act on the mass: there's no air resistance, friction, electromagnetism, nuclear forces, or divine intervention to consider, so the net force is due only to gravity and gravity exerts 1 N.
  5. Sep 20, 2009 #4
    Great- thanks! :smile:
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