I was presented with a very simple physics problem today which unfortunately stumped me for some reason: you have two spaceships: a cruiser weighing a ton, and a battleship weighing 100 tons. Now lets say the cruiser is moving towards the battleship at constant speed. From battleships point of view, the cruiser is coming towards it, so energy in the system is just 1/2 m_cruiser v^2. But from cruisers point of view, the energy in the system is 1/2 m_battleship v^2, which is MUCH greater since m_battleship >> m_cruiser. So the energy in the two systems is different, and yet isn't that exactly the same physical problem? This is such a noob question i almost feel bad asking it.