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Another mechanics question (a simpler one, I proimise!)

  1. Nov 5, 2008 #1
    Another mechanics question :) (a simpler one, I proimise!)

    1. The problem statement, all variables and given/known data

    [​IMG][​IMG]
    As the picture shows:
    M=4kg
    V0=5 m/s
    h=5m
    F(wind)=2N
    angle=15 degrees

    I need to find the distance on axis x of the ball when he hits the ground.

    2. The attempt at a solution

    So this is how I tried to solve it..

    1. I'll try to calculate the distance the ball made untill he got back to the height he started with (the ball goes up a few metters, gets to a point where his speed its 0 and then drops down untill he hits the ground)

    -Mg - F=Ma -> -40-2=4a -> a=-10.5 m/s2 (right?)

    y=yo+v0t+0.5at2
    0=0+5sin15t+0.5*(-10.5)*t2
    -5.25t2+1.3t=0
    t=0.247s

    so to that point the ball made a progress on axis x:
    X1=v*t=5cos15*0.247=1.19m

    Now I need to find his progress on axis x from that point, when he got back to the original height he started with and is falling down 5m.
    The speed on axis y is 5sin15 m/s, so the time it will take the ball to hit the ground from that point is:
    -5=0-5sin15*t+0.5*(-10.5)*t2 (did I get all the minuses right?:shy:)
    5.25t2+1.3t-5=0
    t=0.86s

    so on axis X...
    X2=v*t=5cos15*0.86=4.15m

    and alltogher..
    X1+X2=5.35m

    is there any mistake you can tell I made alond the way?
     
  2. jcsd
  3. Nov 5, 2008 #2
    Re: Another mechanics question :) (a simpler one, I proimise!)

    To check your answer, try doing the problem "all at once" rather than splitting it into two parts. If you get the same answer, it's probably right.
     
  4. Nov 5, 2008 #3
    Re: Another mechanics question :) (a simpler one, I proimise!)

    thanks heth.
    btw, why cant I edit the title? pepole might get the impression that I'm dyslexic.
     
  5. Nov 5, 2008 #4

    Hootenanny

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    Gold Member

    Re: Another mechanics question :) (a simpler one, I proimise!)

    You can edit your posts for a maximum of one hour after they were posted.

    Don't worry about your spelling, we see much worse here :smile:
     
  6. Nov 5, 2008 #5
    Re: Another mechanics question :) (a simpler one, I proimise!)

    My approach about spelling is you cant criticize someone untill you try and write in his language.
    And trust me, hebrew is not an easy one to learn.. :smile:

    BTW
    Its kind of a weird question but are there by any chance people who know Hindi in PF? I'm looking for someone who can translate a few lines from english to Hindi for me :)
     
    Last edited: Nov 5, 2008
  7. Nov 5, 2008 #6
    Re: Another mechanics question :) (a simpler one, I proimise!)

    Hi again! :smile: You might try to post this request in GD (general discussion)? Or look for someone who hints they may be from a country where Hindi is more dominant, and then send them a private message.

    I'll confess to being fluent in only my native tongue, with a small working vocab in just a few romance languages.... mainly to make my kids laugh. I really need to buckle down and get some language-on-tape sets. It would be good to learn more than "Let's go! Hurry up!" "Get on the bus! Have a good day!" or "Good night! Go to bed!" :rofl:
     
  8. Nov 5, 2008 #7
    Re: Another mechanics question :) (a simpler one, I proimise!)

    I am more than willing to help you with your hebrew :)
     
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