cloned33 said:
i have a rc glider measuring 2200 mm on the ground,when in the air it measures about 35mm. Can the the height be calculated from these measurements.
No, the height depends on what distance from the eye the image of the glider measures 35 mm. If you hold a ruler in a stretched hand and the glider seems to measure 35 mm, that's quite different from when hold the ruler right next to your eye. So, 35 mm alone is not a meaningful measurement, you also need to add the distance $d$ from the eye so that that 35 mm at this distance seems like 1200 mm at real distance $h$.
In that case, $h=\frac{1200}{35}d$.
In this regard, I recommend reading a wonderful book "
Physics for Entertainment" (part 2) by Yakov Perelman. In Chapter 9 (p. 210) he says the following.
"A few words, by the by, about the Moon's visible proportions. Ask your friends how big they think the Moon is. You're likely to get a host of different replies. Most will say the Moon is as large as a plate, but some might think it the size of a saucer, an apple, or even a cherry. A schoolboy I once knew always thought the Moon 'as big as a round table covered for twelve' while a certain writer has claimed in a book that the Moon is a 'yard across'.
Why do we differ so much with regard to the size or one and the same thing? Because we
estimate distances differently and moreover subconsciously. A person who takes the Moon to be as large as an apple, imagines it to be much nearer than people who think it the size of a plate or a round table."
