An astronaut in a rocket moving with a speed v = 0.6c relative to Earth performs a collision experiment with two small steel balls and concludes the both momentum and energy are conserved. What would an Earth observer conclude?
A) Only momentum is conserved.
B) Only energy is conserved.
C) Neither energy nor momentum is conserved.
D) Both energy and momentum are conserved.
E) The collision never happened because the two balls are never in the same place at the same time.

Question

Quizplus · Accepted Answer

From the perspective of the astronaut, both momentum and energy are conserved. However, from the perspective of an Earth observer, special relativity must be taken into account because the rocket is moving at a relativistic speed. It can be shown that both momentum and energy are conserved in such collisions in a relativistic framework, which means that an Earth observer would also conclude that both quantities are conserved.

An Astronaut in a Rocket Moving with a Speed V