Today while I am driving my car this question came to my mind but I cannot figure it out. Sorry I am not in physics related major that this question is not expressed professionally.
When you drive a real car you gets less acceleration while at higher speed. But let's say there an engine that get thrust by pushing small particles to a very high speed (near light speed). This engine should get a constant magnitude of force. (Think it as a person throwing a ball, no matter if the person is stationary of riding a car, the person should receive the same magnitude of force). Since the particles' mass is so small so the engine itself should get a constant acceleration no matter what the speed of the engine is.
Say the engine is stationary and use 1 second to accelerate to 10m/s. Then it should use another second to go to 20m/s. But in the second second the engine get's three times more kinetic energy than the first second. This doesn't seem to make sense to me. How can any engine's power rate depend on it's speed? I don't think such photon engine or plasma engine exist right now. But if they come to live one day will it provide a constant thrust?
