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

Posted by TheTriangulum on Apr 27th, 2012

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
Arcones Apr 27 2012, 1:11pm says:

It should be 2807 dots.

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

+2 votes     reply to comment
TheTriangulum
TheTriangulum Apr 27 2012, 2:11pm says:

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

+2 votes     reply to comment
CommanderDG
CommanderDG May 15 2012, 9:00am replied:

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

+2 votes     reply to comment
B7Biscuit
B7Biscuit Apr 27 2012, 3:10pm says:

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.

+4 votes     reply to comment
CommanderDG
CommanderDG Apr 29 2012, 11:40am replied:

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

+1 vote     reply to comment
Arcones
Arcones May 1 2012, 4:13pm replied:

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

+4 votes     reply to comment
CommanderDG
CommanderDG May 15 2012, 9:02am replied:

lol nice!

+2 votes     reply to comment
moretanks!!!
moretanks!!! Jun 2 2012, 10:32am replied:

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

+2 votes     reply to comment
TheTriangulum
TheTriangulum Apr 29 2012, 9:38am says:

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

+2 votes     reply to comment
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