the science class is learning about chemical and physical changes which of the following describes a chemical change

Acompound is found to contain 6.1% hydrogen and 93.9% oxygen. find it’s empirical formula.

All forces cause motion? true or false

In a heat of an engine, if 700 j enters the system, and the piston does 400 j of work what is the final internal (thermal) energy of the system if the initial energy is 1,500 j