Two satellites with equal rest masses of 100 kg are traveling toward each other in deep space. They have identical speeds of 0.600c. The satellites collide and stick together. What is the rest mass of the combined object after the collision?
A) 200 kg
B) 225 kg
C) 250 kg
D) 275 kg
E) 300 kg

Question

Quizplus · Accepted Answer

The rest mass of an object is conserved in all reference frames. Therefore, the rest mass of the combined object after the collision is equal to the sum of the rest masses of the original objects. 
Rest mass of one satellite = 100 kg
Rest mass of two satellites = 200 kg
Therefore, the rest mass of the combined object is also 200 kg.

Two Satellites with Equal Rest Masses of 100 Kg Are