Viewing 15 posts - 1 through 15 (of 15 total)
  • Simple geometry question
  • Dorset_Knob
    Free Member

    If you've got a square-based and square-topped pillar, which is 50cm sq at the bottom, 30 cm sq at the top and 100cm high, what angle do the sides make?

    I was always cr1p at maths.

    Ta!

    kenneththecurtain
    Free Member

    0.46 degrees to vertical

    Wow, I'm bored.

    I can't do trigonometry, but it will be the angle on a 10cm x 100cm triangle, whatever that is, assuming you mean what is the angle of the faces from vertical, not what is the angle at the corners of the trapezium face.

    And, slightly off topic, why do schools always use cm for these type of questions, when everyone in the real world works in mm ?

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    kenneththecurtain
    Free Member

    Actually, I read that as 50cm^2 and 30cm^2 – you probably meant 50*50 and 30*30, in which case that will be wrong.

    Dorset_Knob
    Free Member

    Oh yes, I meant 50*50 and 30*30.

    Now I'm even confused about how I should say that – it's 30cm2, surely?

    No, you're specifying the linear measurements, so it is 30cm square which is 900cm2

    tegski
    Free Member

    As has been said – right angled triangle 10cm at top – 100cm high Tan Ratio gives Tan Angle = 10/100 thus angle = 5.7degrees from vertical.

    Dorset_Knob
    Free Member

    Thanks all.

    Burls72
    Free Member

    Feel free to correct me if i'm wrong but I make it 11.31 deg. The above answer was 10/100 should be 20/100 as the difference is 20cm over the 100cm length. 50cm – 30cm = 20cm, 20 divided by 100 = 5 inv tan = 11.31 deg.

    All 4 sides slope in, so if the top is 20cm smaller than the base, each side slopes in by 10cm.
    Although, now you mention it, that's not specified in the original question. I'm just assuming the two squares are concentric.

    Burls72
    Free Member

    All 4 sides slope in, so if the top is 20cm smaller than the base, each side slopes in by 10cm.
    Although, now you mention it, that's not specified in the original question. I'm just assuming the two squares are concentric.

    It would make more sense than my answer.

    I was always cr1p at maths.

    +1 😳

    adeward
    Free Member

    i always use mm in design and technology and it's them mafs and science bods who use cm,,,

    often get students and teachers looking confused at a small square of wood when they asked me for something 50 X 50 I know what they realy want but i like being awkward sometimes

    MM are the standard unit of measurement in engineering and construction.
    Schools are just confusing kids by teaching them to use CM.
    Nobody sells 0.8cm x 2.5cm bolts or 5cm x 7.5cm timber.

    Possibly an urban myth, but I heard of someone who wanted an adapter made to connect a round flue to the oval outlet of a stove.
    He did a nice little sketch with measurements, but not the units, and handed it to the steel fabricator.
    It came back exactly 2.54 times the size it should have been. 😀

    kenneththecurtain
    Free Member

    MM are the standard unit of measurement in engineering and construction.
    Schools are just confusing kids by teaching them to use CM.

    [pedant] No it's not, mm is though [/pedant] 🙂

    RealMan
    Free Member

    MM are the standard unit of measurement in engineering and construction.
    Schools are just confusing kids by teaching them to use CM.

    Both are stupid, it should all be done in meters as that's the SI unit. 😉

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