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Homework Help: Time of a projectile

  1. Nov 1, 2011 #1
    Problem solved, many thanks
     
    Last edited: Nov 1, 2011
  2. jcsd
  3. Nov 1, 2011 #2
    Write down some equations that may be used. The we can discuss which of them can apply.
     
  4. Nov 1, 2011 #3
    You might want to check your units.
     
  5. Nov 1, 2011 #4
    I'm really not sure what equations to use. I have a list of some equations but they ask for the initial velocity.
     
  6. Nov 1, 2011 #5
    You can find the initial speed in the vertical direction.
     
  7. Nov 1, 2011 #6
    Could you explain that please?
     
  8. Nov 1, 2011 #7
    Try to find what is known in the vertical direction.
     
  9. Nov 1, 2011 #8
    Vertical displacement is 15m, and Gravity due to acceleration is 9.8 m s^2
     
  10. Nov 1, 2011 #9
    initial speed
    final speed
    distance travelled
    acceleration
    time
    Which of the above are known in the vertical direction?
     
  11. Nov 1, 2011 #10
    What is the speed in the vertical at the maximum height?
     
  12. Nov 1, 2011 #11
    Distance Travelled, and Acceleration?

    Feel like I'm missing something here...
     
  13. Nov 1, 2011 #12
    Correct but acceleration is negative if we choose upward direction as positive.
     
  14. Nov 1, 2011 #13
    Oh zero. I was missing something
     
  15. Nov 1, 2011 #14
    Now you CAN find the initial speed in the vertical direction.
     
    Last edited: Nov 1, 2011
  16. Nov 1, 2011 #15
    Before I calculate the final speed, I have to get t, correct? So, am I write in believing this is 15m/-9.8 m s^2
     
  17. Nov 1, 2011 #16
    I think that you mean the initial (vertical) speed.
     
  18. Nov 1, 2011 #17
    Yes, I did.
     
  19. Nov 1, 2011 #18
    If you know the initial and final vertical speeds, and the vertical distance you can find the time which is the quantity that you originally wanted to find.
     
  20. Nov 1, 2011 #19
    Sorry, I'm having a hard time getting my head round this.
    I'm not sure what equation to use to find final velocity.
     
  21. Nov 1, 2011 #20
    You will only learn how to do physics only if you try to pick the equation yourself.
    Try to find - from notes or internet - the equations you can use.
     
  22. Nov 1, 2011 #21
    OK, I've got the equation for final velocity, give me a minute and i'll work out the time.
     
  23. Nov 1, 2011 #22
    Ok, so now I have the time, am I right in believe the total time for the projectile will be the time i've just calculated, x2?
     
  24. Nov 1, 2011 #23
    Yes.
     
  25. Nov 1, 2011 #24
    Brilliant! Thanks, Now i've got to work out the launch speed.... :-/

    I'm going to double check my notes, but i'm sure i'll need help sooner or later.
     
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