Please choose the correct answer to the question: A perpetual motion machine is a theoretical device which, once started, continues to operate without any additional input of energy. Which statement describes why a perpetual motion machine is impossible to design?

Answer1: Energy can be converted into mass. Answer2: Friction reduces the efficiency in a system. Answer3: The amount of energy in a system remains constant. Answer4: Potential energy can be converted into kinetic energy.

Answer format: answer1/answer2/answer3/answer4