Explain why you move forward and a boat moves backward when you jump from a boat to a pier?

In a heat engine if 1000 j of heat enters the system the piston does 500 j of work, what is the final internal energy of the system if the initial energy was 2000 j ?

(**i would really appreciate if this was answered soon** ) which pair of quantities includes one quantity that increases as the other decreases during simple harmonic motion?

Achlorine atom has 17 protons and 18 neutrons. what is its mass number? what is its atomic number?