Answer:
The answer is given below
Explanation:
u is the initial velocity, v is the final velocity. Given that:

a)
The final velocity of cart 1 after collision is given as:

The final velocity of cart 2 after collision is given as:

b) Using the law of conservation of energy:

Answer:
The answer <em><u>is C. Mars</u></em>. Mars and Mercury are both smaller than Earth's core. Hope this helps you :)
Well, one is more effeciant than the other. I think it would run on less gass.