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Question about speed of the flying body

  1. May 9, 2015 #1
    I tried to find an answer everywhere but didn't found it and I am not strong at physics so please help me 4xH3vjF.png

    I need to know equations for minimum speed required for some body to fly horizontally depending on it's mass , height of fligth and distance to fly . I mean object must travel some distance straight - without falling an inch - sustaining it's height during some given distance. As I understand subject - heavier bodies need higher speed to counter gravity to sustain their flight or they will simply fall or something like that. Is there any equations to find this speed if I know mass, height and distance?...object is bullet-shaped and all his dimensions is known. roughly mass is 800 000 kg , height is 5 m and distance is 100 m.

    Can anybody help me with that?...
     
  2. jcsd
  3. May 9, 2015 #2

    davenn

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    hi
    welcome to PF

    are you referring to something with or without wings ?
     
  4. May 9, 2015 #3
    Hey! w/o wings. Body got shot from cannon. Body have no rocket propulsion as well. It's just body in form of a bullet on his own. :)
     
  5. May 9, 2015 #4

    davenn

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    800,000 kgs is a huge object a decent sized ship
     
  6. May 9, 2015 #5
    It's giant bullet ;) Any ideas for equations?
     
  7. May 9, 2015 #6

    russ_watters

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    An object cannot fly horizontally without lift from wings or cotinuous thrust.
     
  8. May 9, 2015 #7

    Bandersnatch

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    What if you had a spinning bullet with some angle of attack to its flight? That should generate some lift.
     
  9. May 9, 2015 #8
    How bullets fly horizontally then? :O They are not declining up to some point...
     
  10. May 9, 2015 #9

    Bandersnatch

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    Why do you think they aren't?
     
  11. May 9, 2015 #10
    Maybe you just got me wrong? Hm - object moves at some height.
     
  12. May 9, 2015 #11

    russ_watters

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    Fair enough: or some lift generating mechanism like a lifting body or spin perpendicular to the direction of flight (for the bullet, the spin does not generate the lift, it just makes it stable -- the angle of attack may generate lift).

    Generally, though, that doesn't happen for bullets.
     
  13. May 9, 2015 #12
    Because you can precisely hit a target with them.. I mean not declining drastically up to some point.
     
  14. May 9, 2015 #13

    russ_watters

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    In general, bullets follow a ballistic path.
    Incorrect: gun sights on bullets that travel any significant distance are adjusted to elevate the bullet's path.
     
  15. May 9, 2015 #14
    Is there any equations for this?...
     
  16. May 9, 2015 #15

    russ_watters

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  17. May 9, 2015 #16
    This DO NOT consider MASS !

    I need equation for projectile speed which will consider it's mass too as I say in OP.
     
  18. May 9, 2015 #17

    Bandersnatch

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    I'd rather say that it's not very significant here, not that it doesn't happen. Just a minor nitpick.

    @VioletHood once in flight, and when air resistance can be neglected, the mass of the projectile doesn't matter. It's the same idea as with Galileo's observation that all objects fall at the same rate regardless of mass (again, disregarding air resistance).

    If air resistance is to be included, which for low speeds and huge, compact mass as in the OP could very well be neglected, the equation of motion does include mass, but is also much more involved than the basic no-drag equation:
    http://en.wikipedia.org/wiki/Trajec...rajectory_of_a_projectile_with_air_resistance

    The above still disregards any lift generated by the angle of attack of the bullet, but again, that's not at all significant an effect unless you're talking about orbital velocities.
     
  19. May 9, 2015 #18

    russ_watters

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    Mass is not relevant to the basic projectile motion equation because acceleration due to gravity is the same for all objects. The only impact mass might have for an object that doesn't generate lift is if drag is considered and the drag vs mass mix results in a different deceleration.
     
  20. May 9, 2015 #19
    Too complex equation for me. xD Can you simplify it or it's impossible to fulfill my demand?

    I always thought that make million ton projectile fly requires magnitudes bigger speed. o_O
     
  21. May 9, 2015 #20

    russ_watters

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    I'm sorry, but your question is based on a false premise, so it is not possible to fulfill your demand: you cannot make an object fly horizontal without lift (with speed alone).
     
  22. May 9, 2015 #21
    I don't mean projectile should not fall at all. I allow him to lose some height - 10-20% during it's flight with distance of 100 m.

    Ok if it's too complicated. I just want to know speed of my projectile to flew 100 mters and consider it's mass too.
     
  23. May 9, 2015 #22

    russ_watters

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    OK, well that you can easily find using the projectile motion equations. Pick an exact fall distance, then give a try at using the equations provided to figure it out. Let us know if you get stuck.
     
  24. May 9, 2015 #23
    russ watters and other guys who tried to help me, sorry - I am too noob for this and currently waiting for simple ready solution by much more competent people. :)

    One person perfectly rephrased what I wanted to find out and this should change case.

    Well the task consists in, that a body weighing 750 000 kg. started horizontally with some speed with height of 3 meters and after 100 meters of flight didn't fall lower then 2.5 meters. Question: "What speed is necessary for this person?"

    Can someone help me now?
     
  25. May 10, 2015 #24

    russ_watters

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    Sorry, but that isn't how we do things here. This forum is for learning, not for getting other people to do the work for you. So please make an effort to learn from the information already provided. As I said, we'll help you if you get stuck.
     
  26. May 11, 2015 #25
    Though mass is irrevelant for my question right? Problem is to make heavy body move at some speed and it will behave totally similar to lighter body in that case as I understood from another forum.
     
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