MHB Calculating Height of RC Glider from Ground and Air Measurements

[cloned33]

Hello,just seeing if someone can help me on here,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.

 

[Ackbach]

Hello, just seeing if someone can help me on here. I have a rc glider measuring 2200 mm on the ground; when in the air it

What do you mean by "it" here? The shadow on the ground? Or the silhouette?

 

[Evgeny.Makarov]

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 $h$.

View attachment 3414​

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."

 

[cloned33]

What do you mean by "it" here? The shadow on the ground? Or the silhouette?

hello,im not into maths but ill try to explain what I want to solve. if I met you and I thought you was 6foot tall, if you then walked away from me till you only looked 1inch tall,whats the distance from where you stood to where you stopped

 

[cloned33]

thank you for the reply,I see I need to go back to school this all seems way above my head.to me it seemed a straight forward calculation but nothings simple these days regards martin