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Free fall question, 2 objects meet

  1. Jun 10, 2015 #1

    Radic S

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    1. The problem statement, all variables and given/known data
    Object A has VA =20m/s going downwards, Object B has VB=20m/s going upwards. Only gravity is given and they are traveling along a straight line vertically. What is the Δt when they meet and what Δd for object B.

    2. Relevant equations
    5 Kinematic equations + v=Δd/Δt,a=Δv/Δt

    3. The attempt at a solution
    I've tried numerous ways to approach this problem, i've concluded that they will meet each other when both times are equal to each other but I dont know how to resolve that given the equations I have. I've tried substituting equations, subtracting, using the quadratic formula to no avail. I'm looking at some advice at how I can understand this problem to improve my grasp of physics, i'm not looking for the answer. I've worked at this for about 4 hours and nothing has come from it, any hits/suggestions would be appreciated.
     
  2. jcsd
  3. Jun 10, 2015 #2

    mfb

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    What is their initial position? If they start at the same position they will never meet.
    Both are in free fall?

    Their positions are the same as well.
    Please show your work, otherwise it is impossible to tell what went wrong.
     
  4. Jun 10, 2015 #3

    Radic S

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    Object A is above object B that's all the information I have that is given. I can add what work i've tried so far but it will be a lengthy add, if it will help I can do it no problem

    11hvuvr.jpg
     
  5. Jun 10, 2015 #4

    mfb

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    If you don't know their initial separation you cannot get a reasonable answer. You can invent a variable and solve using this variable, of course, but that's not the way homework questions are supposed to work.
    Can you copy the exact original homework question?
     
  6. Jun 10, 2015 #5

    Radic S

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    I'm sorry mfb there isn't anything else to copy which is why I came here hoping to find some sort of hint. My teacher just wrote it on a piece of paper the same way I drew it with both velocities and only gravity working with it. It's bonus class work so I'd have to take a photo of it and post it tomorrow but you won't find it any useful.
     
  7. Jun 10, 2015 #6

    Radic S

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    The thing is also I haven't done calculus yet and this is a grade 11 physics class so I'm fairly new at this.
     
  8. Jun 10, 2015 #7

    mfb

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    Then I don't think the question makes sense.
    You can introduce some variable for the initial height difference and find the collision time. Hint: this is very simple with the right idea.
    What does Δd even mean?
     
  9. Jun 10, 2015 #8

    Radic S

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    Δd means change df-di, it's the Greek delta sign. I thought about introducing some distance variables but when I dont know the relative position of object A/B i dont understand what i'd find with that? i've used the quadratic equation when I assumed the height was 1 and it didn't get me closer to solving the problem.
     
  10. Jun 10, 2015 #9

    Radic S

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    The 2. Relevant equations I wasn't given with the question, I added those to the list of equations that I was attempting to use to solve the problem.
     
  11. Jun 17, 2015 #10

    Radic S

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    Wanted to update you about the question. I threw in the towel finally with the question and while she was explaining to me how to solve the question I mentioned we can't solve it in that manner because we dont have position/displacement. It turns out she made a mistake and forgot to give me that information.
     
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