Is an electric toothbrush input energy equal yo useful output energy?

No, an electric toothbrush's input energy is not equal to its useful output energy. Like all machines, electric toothbrushes are not 100% efficient, meaning that some of the input energy is lost as waste heat and sound. The efficiency of an electric toothbrush is determined by the ratio of useful output energy (the mechanical energy used to clean teeth) to the total input energy (the electrical energy consumed by the toothbrush). The efficiency of electric toothbrushes can vary depending on factors such as the design and quality of the toothbrush, the type of battery used, and the user's brushing habits.