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Homework Help: Height, hangtime, and range during frictionless freefall.

  1. Nov 30, 2005 #1
    Ok, so I've got this physics question on a review sheet for a test tomorrow...and I keep getting a bunch of random answers that don't make sense...see if you can help me...

    Someone kicks the football from ground level (0 meters) with an initial velocity of 32 meters/second, 34 degrees above the horizontal axis. Find the hangtime of the ball (time in the air), the range (how far it goes) and the max height. Assume air resistance is negligible (no air friction, just gravity).

    I just have no idea where i put this 34 degrees into my equations...

    And we're using 9.8m/s2 for gravity.

    And in yalls opinion, what's the best place to start this question? Hang time, range or max height?
  2. jcsd
  3. Nov 30, 2005 #2
    Id recomend trying to use some equations. Write what you think you should use and WHY.
  4. Nov 30, 2005 #3


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    Homework Helper

    Look up kinematic equations for projectile motion (It's basicly working a constant velocity motion and a uniform acceleration motion).
  5. Nov 30, 2005 #4
    there are only two equations of motion.
    find those.
    eliminate time between them and you can get a third.

    where to put the angle: did you draw a picture? did you draw the velocity and acceleration vectors?

    what to start with: if you know what is happening to the ball, then this is really really easy. what is hang time?
  6. Nov 30, 2005 #5

    thank you.....*goes to find those equations*.....suggestions?
  7. Nov 30, 2005 #6
    kinematics. motion under a constant force.
  8. Nov 30, 2005 #7
    If you cant do that, Id recomend reading your book before attempting to do the homework and asking others to do it for you. Read about particle motion, most likely chapter 2-3 or so.
  9. Nov 30, 2005 #8

    well..i've got a test tomorrow...so i'd like to know how to do the problems myself...I am not asking for others to do it for me...but just to get me started...that seems to help...i pay attention in class...and our teacher has never given us a problem like this before...but I looked up a couple formulas...and this is what i got...






    Max Height:

  10. Nov 30, 2005 #9
    I hope you got your anwser by understanding why and how you use those equations and did not just plug into an example problem in the book that was very simliar, 4 posts ago you did not even know what equations to use and now you have the anwser done.....?
  11. Nov 30, 2005 #10

    well....i took what we did from vectors in the first couple units and applied those....i understood vectors...so once i put everything in components...everything seemed to work....anything wrong there?....and by the way i haven't brought my textbook home all year...our teacher doesn't like it...and she teaches above what's in there...
  12. Nov 30, 2005 #11
    As long as you know what your doing and did the work yourself. It just seemed odd that you did not even know which equations to use and all of a sudden you solved it like magic in a mere 5 mins. Your method of applying vectors is correct. As for not bringing your book home, I cant imagine why you would not care to take it home so that you have a reference at the very least.
  13. Nov 30, 2005 #12
    if you use the 2 kinematic equations and eliminate time between them you get an expression for max height that has 3 terms. None of them have angles. Once you do this, you will be able to know the max height for ANY projectile if you know what Vinitial is.

    what it looks like you've done is, is go back to example problem and change the numbers.
    are you going to be able to do it when you don't have the example problem?
    do you know why it's cos for x and sin for y?

    if you don't know how to draw a picture and label it with appropriate vectors, you will have problems forever because the first step is always draw the picture.
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