The Tennessee Valley Authority's coal-fired Kingston plant in Tennessee generates 10 billion kilowatt-hours a year by burning 13,000 metric tons of coal a day, supplying electricity to almost 700,000 homes. If all of the 7.7 billion metric tons of coal consumed worldwide in 2015 was converted to electricity, it would have produced approximately billion kilowatt-hours of electricity. Assume the same efficiency as the Kingston plant.

Aparticle's position is given by x = 3.00 - 9.00t + 3t2, in which x is in meters and t is in seconds. (a) what is its velocity at t = 1 s? (b) is it moving in the positive or negative direction of x just then? (c) what is its speed just then? (d) is the speed increasing or decreasing just then? (try answering the next two questions without further calculation.) (e) is there ever an instant when the velocity is zero? if so, give the time t; if not, answer "0". (f) is there a time after t = 3 s when the particle is moving in the negative direction of x? if so, give the time t; if not, answer "0".

Scientific models are based on current knowledge, which can limit their effectiveness when new discoveries are made.

An atom that has gained or lost electrons is called an _