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Homework Help: Time of a projectile

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  1. Nov 1, 2011 #1

    MrRandom66

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    Problem solved, many thanks
     
    Last edited: Nov 1, 2011
    MrRandom66, Nov 1, 2011
  2. jcsd
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  3. Nov 1, 2011 #2

    grzz

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    Write down some equations that may be used. The we can discuss which of them can apply.
     
    grzz, Nov 1, 2011
  4. Nov 1, 2011 #3

    obafgkmrns

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    You might want to check your units.
     
    obafgkmrns, Nov 1, 2011
  5. Nov 1, 2011 #4

    MrRandom66

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    I'm really not sure what equations to use. I have a list of some equations but they ask for the initial velocity.
     
    MrRandom66, Nov 1, 2011
  6. Nov 1, 2011 #5

    grzz

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    You can find the initial speed in the vertical direction.
     
    grzz, Nov 1, 2011
  7. Nov 1, 2011 #6

    MrRandom66

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    Could you explain that please?
     
    MrRandom66, Nov 1, 2011
  8. Nov 1, 2011 #7

    grzz

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    Try to find what is known in the vertical direction.
     
    grzz, Nov 1, 2011
  9. Nov 1, 2011 #8

    MrRandom66

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    Vertical displacement is 15m, and Gravity due to acceleration is 9.8 m s^2
     
    MrRandom66, Nov 1, 2011
  10. Nov 1, 2011 #9

    grzz

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    initial speed
    final speed
    distance travelled
    acceleration
    time
    Which of the above are known in the vertical direction?
     
    grzz, Nov 1, 2011
  11. Nov 1, 2011 #10

    grzz

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    What is the speed in the vertical at the maximum height?
     
    grzz, Nov 1, 2011
  12. Nov 1, 2011 #11

    MrRandom66

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    Distance Travelled, and Acceleration?

    Feel like I'm missing something here...
     
    MrRandom66, Nov 1, 2011
  13. Nov 1, 2011 #12

    grzz

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    Correct but acceleration is negative if we choose upward direction as positive.
     
    grzz, Nov 1, 2011
  14. Nov 1, 2011 #13

    MrRandom66

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    Oh zero. I was missing something
     
    MrRandom66, Nov 1, 2011
  15. Nov 1, 2011 #14

    grzz

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    Now you CAN find the initial speed in the vertical direction.
     
    Last edited: Nov 1, 2011
    grzz, Nov 1, 2011
  16. Nov 1, 2011 #15

    MrRandom66

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    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
     
    MrRandom66, Nov 1, 2011
  17. Nov 1, 2011 #16

    grzz

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    I think that you mean the initial (vertical) speed.
     
    grzz, Nov 1, 2011
  18. Nov 1, 2011 #17

    MrRandom66

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    Yes, I did.
     
    MrRandom66, Nov 1, 2011
  19. Nov 1, 2011 #18

    grzz

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    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.
     
    grzz, Nov 1, 2011
  20. Nov 1, 2011 #19

    MrRandom66

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    Sorry, I'm having a hard time getting my head round this.
    I'm not sure what equation to use to find final velocity.
     
    MrRandom66, Nov 1, 2011
  21. Nov 1, 2011 #20

    grzz

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    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.
     
    grzz, Nov 1, 2011
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