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Can you do the test? lol lol lol lol lol lol lol lol

Posted by on

Find out how many dots are here in at least 2 minutes
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question 2
An astronomer measures the wavelength of an absorption line in the
spectrum of light from a galaxy to be 720.6 nm.
If the true wavelength of the spectral line is 654.8 nm, calculate the
radial velocity of the galaxy.

Post comment Comments
Arcones Creator
Arcones

It should be 2807 dots.

And that was under two minutes. I'll let someone else take question 2 :P

Reply Good karma+2 votes
TheTriangulum Author
TheTriangulum

Well done! - one off though

solution for question 1: triangular sequences:
2x(0.5(n^2+n)) = 1 period
therefore 4 periods = number of dots
In this case...
n = 26
so...
2x(0.5(26^2+26) = 702
There are 4 periods hence:
702x4 = 2808

Reply Good karma+2 votes
CommanderDG Creator
CommanderDG

Actually it's 2807 as he mentioned because there is missing a point on the top line.

Reply Good karma+2 votes
B7Biscuit
B7Biscuit

I got 2807 too, but I cheated: I just counted the number of dots in the longest row, used a calculator to add consecutively, multiplied, and subtracted the one - no maths for me thankyou.

Reply Good karma Bad karma+4 votes
CommanderDG Creator
CommanderDG

I did the same =P.(question 1).

Reply Good karma+1 vote
Arcones Creator
Arcones

lol, I just copied and pasted into a word doc xD

Reply Good karma+4 votes
CommanderDG Creator
CommanderDG

lol nice!

Reply Good karma+2 votes
moretanks!!!
moretanks!!!

I can't the only one who didn't cheat...

Reply Good karma Bad karma+2 votes
TheTriangulum Author
TheTriangulum

Question 2 solution:

The simplest way is to use the two values of wavelength to calculate the ratio:
wavelegnth 720.6 nm – 654.8 nm
= = 0.10(048…)
wavelength 0 654.8 nm

This value can now be equated to v/c

and so we now re-arrange to give v = 0.10 x c

= 0.10 x 300 000 km/s (the value of the speed of light)

= 30 000 km/s

Answer: 30 000 km/s

Reply Good karma+2 votes
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