This question is super tricky for me, please help!

Question

An observer views four identical objects that are traveling at speeds close to the speed of light. Can their lengths be used to rank the objects according to their speeds?
A. No. The length of each object depends on the frame of reference of the observer.

B. No. The lengths of the four objects should be the same regardless of speed.

C. Yes. The shortest object is traveling the most slowly.

D. Yes. The longest object is traveling the most slowly.

Answer 1

c = speed of light

 

v = speed of object

 

L0 = length of object when at rest

 

L = length of object when moving at speed v

 

According to special relativity,

 

L = L0 * sqrt[1 - (v/c)^2]

 

L < L0, so tho faster object will appear shorter than the slower object, i.e. the slower object will appear longer than the faster object, which is answer (D)