Two cars with the same mass m are moving at speeds v and 3v relative to the Earth in the same direction.

Two cars with the same mass m are moving at speeds v and 3v relative to the Earth in the same direction. What is the kinetic energy of the second car in the reporting system associated with the first?

Ek is found by the formula:
0.5 mV ^ 2
It follows from the question that we need to find Ek2 / Ek1
Since the masses are the same, they will shrink. Also shrink 0.5
After the contractions, we get the ratio of the speeds squared. I.e:
V2 ^ 2 / V1 ^ 2
V2 = 3V1
Hence: 9V1 / V1 = 9 (J)