An observer sees two spaceships, S1 and S2, each having the same ...

[Sportsfan2111]

An observer sees two spaceships, S1 and S2, each having the same length in its own rest frame, traveling toward each other along parallel lines from opposite directions, with equal speeds relative to the observer.
 
  As seen by this observer, the two spaceships have the same length and, when they are next to each other, the nose of one coincides with the tail of the other, and vice-versa. However, as seen by passengers on either one of the spaceships, the other spaceship is shorter than their own, so if the tail of the other spaceship is in line with the nose of their spaceship, the nose of the other spaceship cannot be lined up with the tail of theirs. How can you explain this discrepancy?

Question 2

The reaction 2H + 2H  3H + 1H releases 4.03 MeV of energy. If one kilogram of deuterium were made to go through this reaction, how much energy would be produced?
 
  A)
 
  9.7  107 J
  B)
 
  9.7  1013 J
  C)
 
  1.9  107 J
  D)
 
  1.9  1014 J
  E)
 
  1.9  1011 J

[frogdreck123456]

Answer to Question 1

Events that are simultaneous in one frame of reference are not simultaneous in a reference frame that is moving relative to the first. If we call the event A the coincidence of the nose of S1 and the tail of S2, and event B the coincidence of the nose of S2 and the tail of S1, then, according to the passengers in S1, A occurs before B, while according to the passengers in S2, B precedes A. Finally, the observer who saw them traveling towards each other sees the two events as simultaneous.

Answer to Question 2

B

[Sportsfan2111]

Excellent

[raili21]

Gracias!