Doppler Effect - Blue Shift

[MedPR]

---

Members do not see this ad.

Ok this is a hypothetical question about a roman numeral question.

In a nutshell, the question is as follows.

A blue-shift indicates:

I. star could be moving towards the Earth
II. star could be moving away from the Earth
III. Earth could be moving towards the star
IV. Earth could be orbiting the star in a perfectly circular path

A. I only
B. II only
C. I and III only
D. II and IV only

Based on the answer choices, C is the best answer. Blue shift = higher frequency = objects approaching each other. Basically the definition of the Doppler Effect.

However, what if one of the answers had been I, II, and III? II could be true if the Earth was moving toward the star faster than the star was moving away from the Earth. Right?

 

[Ssina]

yeah it would, but I'll doubt they'll be that vague (or that's probably why there is not I, II, III)

 

[MedPR]

yeah it would, but I'll doubt they'll be that vague (or that's probably why there is not I, II, III)

Yea it seemed like it could be one of those tricky MCAT questions. When I initially read through the roman numeral answers I immediately looked for a "I, II, and III" option in the A-D answers. To me it's like a projectile motion question that asks you what the velocity is at the apex of a cannon ball initially shot out of a cannon at a 30 degree angle. One of the answers is always v=0 and it's there to trick people who forget about the x component of the velocity. You know, since the y component of velocity is always 0 at the apex of a projectile.

 

[Ssina]

most definitely... that used to be me.. picking confidently v as 0!!
BUT I SAY NO MORE SIR! (well at least for couple of month after the MCAT, till I officially forget everything)

 

[MedPR]

most definitely... that used to be me.. picking confidently v as 0!!
BUT I SAY NO MORE SIR! (well at least for couple of month after the MCAT, till I officially forget everything)

Me too. I used to hate those trick questions, but I love them now because I won't fall for it on the real thing 🙂