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Projectiles Question

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  1. Jul 14, 2014 #1
    1. The problem statement, all variables and given/known data

    As part of a NASA experiment, golfer Tiger Woods drives a golf ball on the moon, where
    g = 1.60 m/s2. He ‘launches’ a golf ball with a speed of 285 km/h, at an angle of 42o with the horizontal. What horizontal distance will his drive travel before landing back on the surface of the moon. Ignore the curvature of the moon.


    2. Relevant equations

    d = (Vi)(t) + 1/2(a)t2

    Vf =Vi + at

    (Vf)2 = (Vi)2 + 2ad

    3. The attempt at a solution

    Initial horizontal velocity:

    285 x cos42
    = 211.8 km/h

    Initial Vertical Velocity

    285 x sin42
    = 190.7 km/h

    Finding time using vertical components

    d = (Vi)(t) + 1/2(a)t2

    0 = 190.7t - 4.9t2

    t = 38.9 s

    Using time to find distance

    d = (Vi)(t) + 1/2(a)t2

    d = 211.8 x 38.9 + 1/2(0)t2

    d = 8239 m
     
  2. jcsd
  3. Jul 14, 2014 #2

    haruspex

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    4.9?
     
  4. Jul 14, 2014 #3
    Sorry, I skipped a step. 1/2 x 9.8 = 4.9
     
  5. Jul 14, 2014 #4

    Nathanael

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    Haruspex is a smart guy, I'm sure he could see the step you skipped.

    His next question would be:

    "9.8?"
     
  6. Jul 14, 2014 #5

    Nathanael

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    Besides that, though, there's one more small problem. Your units are inconsistent.

    (You need to convert km/hr to meters/second)
     
  7. Jul 14, 2014 #6
    Thanks! I completely missed that. My final answer is 635 m
     
  8. Jul 14, 2014 #7

    Nathanael

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    My answer disagrees.

    How long will the ball be in the air? (What was your calculation for this?)
     
  9. Jul 14, 2014 #8
    10.8 s ?
     
    Last edited: Jul 14, 2014
  10. Jul 14, 2014 #9
    d = (Vi)(t) + 1/2(a)t2

    0 = 52.97t - 4.9t2

    t = 10.8 s
     
  11. Jul 14, 2014 #10

    Nathanael

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    Have you forgotten where this is taking place? :) Remember, we're not on Earth.
     
  12. Jul 14, 2014 #11
    d = (Vi)(t) + 1/2(a)t2

    0 = 52.97t - 0.8t2

    t = 66.21 s

    I had forgotten! Thank you so much!
     
  13. Jul 14, 2014 #12
    Final answer is 3.9 km
     
  14. Jul 14, 2014 #13

    Nathanael

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    There you go, that should be the correct answer.

    (Do you have something that says what the correct answer is?)
     
  15. Jul 14, 2014 #14
    Yup! That's what it says the answer is.
     
  16. Jul 17, 2014 #15
    You have missed out on crucial piece of information which the value of is 1.60m/s^2 as the event is taking place on the moon
     
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