I wrote this physics-astronomy-math question for a presentation but I’m not sure I solved it correctly myself. It’s not hard, just a lot of conversions.
The observed wavelength is 900000 inches, while its rest wavelength is 460 picoparsecs. How fast is the object moving, in knots?
I recognize that the object ends up moving faster than the speed of light.
Thanks for your help.
We don’t do homework here. If you actually wrote the question, I’m worried that you don’t know enough about the subject you’re teaching to be teaching it correctly, but I will say I’m quite sure you didn’t solve it correctly if you determined the speed to be faster than c.
OOOOOOOOPS, my bad, I got just under c, 5.83x 10^8 knots.
Like OldGuy, I’m really not sure what you mean. Certainly you’re not using standard physics language correctly (and I say this as a physics professor). For example, what do you mean by “rest wavelength”?
I’m guessing that the object in question emits light of some frequency (a spectral line, or something of the sort), and that the rest wavelength is the wavelength measured in a reference frame where the object is at rest.
Ah, that seems obvious now. In my defense, I was posting past my bedtime.
In which case: Cardboard, if you’re using the relativistic Doppler shift formula, you can’t get a speed greater than c for the speed of the observer; if you did, you did your algebra wrong. Thankfully, you seem to have corrected your error.
I know nothing about wave physics, but as long as we are calculating conversions:
I always enjoy pointing out that the speed of light can be precisely converted to
c =1.98287925 × 10^14
if you are using units of : fathoms per fortnight.
(with thanks to the author of The Know-it-All for some fine bathroom reading while preparing for a colonoscopy)
I thought everyone knew that in the FFF system the unit of length is the furlong not the fathom. The speed of light is 1.8 terafurlongs per fortnight.