Based on the second law of thermodynamics why must a machine always be less than 100% efficient?
a. heat never moves from cold to hot.
b. heat is never converted completely into mechanical energy.
c. heat never flows from hot to cold.
d. entropy never increases.

Which statement is true? a. kepler's laws apply only to the motion of earth. b. kepler's laws can be used to predict eclipses. c. kepler's laws are true for a central force that is directly proportional to distance. d. kepler's laws can be deduced from newton's laws of motion and gravity.

The junction rule describes the conservation of which quantity? note that this rule applies only to circuits that are in a steady state.

Energy transformations that involve one transformation from one type of energy to another are called transformations.