Advertisement
If you have a new account but are having problems posting or verifying your account, please email us on hello@boards.ie for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact hello@boards.ie

How far is the horizon?

Options
  • 17-06-2012 10:33pm
    #1
    charles_92688
    Registered Users Posts: 52 ✭✭


    On our perfectly spherical 25000 circumference "earth", a man 6'2" tall (eye balls are 6 feet above the ground), how far is the horizon from the man?

    No calculators. (We're trying to get people to guesstimate.)

    PS. I asked my dad this question and he got it correct in three seconds. Caveat, he was an engineer who worked on radio transmitters and antenna.


Comments

  • Options
    #2
    im invisible
    Closed Accounts Posts: 4,372 ✭✭✭im invisible


    well, as we're guessing, and its too late to be trying this in my head, i'd say 4 or 5 miles, i'll go with 4


  • Options
    #3
    stoneill
    Registered Users Posts: 3,610 ✭✭✭stoneill


    1.22 x sqrt(h) or about 3 miles.


  • Options
    #4
    im invisible
    Closed Accounts Posts: 4,372 ✭✭✭im invisible


    i worked it out, and its less than you'd think

    also, my eye line is about 5 inches from the top of my head, so we'll make yer man 6' 5"


  • Options
    #5
    3DataModem
    Registered Users Posts: 3,957 ✭✭✭3DataModem


    25000 miles is 40000 k or 40000000 metres

    So 40m metre circumference means a 40m divided by twice pi... So about 6m metres.

    Assume the guy is 2 metres tall to eyes

    So 6000002 squared minus 6000000 squared is about 24 million, and the square root of that is about 4,900

    So... I say 5 kilometres

    Assuming the guy is at sea level of course. You need to define the problems better.


  • Options
    #6
    charles_92688
    Registered Users Posts: 52 ✭✭charles_92688


    3DataModem wrote: »
    25000 miles is 40000 k or 40000000 metres

    So 40m metre circumference means a 40m divided by twice pi... So about 6m metres.

    Assume the guy is 2 metres tall to eyes

    So 6000002 squared minus 6000000 squared is about 24 million, and the square root of that is about 4,900

    So... I say 5 kilometres

    Assuming the guy is at sea level of course. You need to define the problems better.
    You need to read the posts better. We wrote in the original post that the earth was a perfect sphere so there is no assumption of sea level.

    But you are correct; it is about three miles away.


  • Advertisement
  • Options
    #7
    3DataModem
    Registered Users Posts: 3,957 ✭✭✭3DataModem


    charles_92688 wrote: »
    You need to read the posts better. We wrote in the original post that the earth was a perfect sphere so there is no assumption of sea level.

    So what if he's upstairs? Or sitting? I understood what you meant of course, I was just putting the caveat on my answer, not your question.


  • Options
    #8
    Hogzy
    Registered Users Posts: 7,544 ✭✭✭Hogzy


    Im going to say 3-4 miles?


  • Options
    #9
    Trippie
    Registered Users Posts: 1,993 ✭✭✭Trippie


    I take it we all watched that episode of QI so


  • Options
    #10
    charles_92688
    Registered Users Posts: 52 ✭✭charles_92688


    Hogzy wrote: »
    Im going to say 3-4 miles?

    Yep, that's about right. I thought that was hard to believe probably because we can see mountains 50 miles away - you get the impression the world is "flat".


Advertisement