Calculate the efficiency of a fossil-fuel power plant that consumes 380 metric tons of coal each hour to produce useful work at the rate of 720 mw. the heat of combustion of coal (the heat due to burning it) is 28 mj/kg.

24.35 %

Explanation:

m = 380 metric tons = 380 x 10^3 kg , time = 1 hour = 3600 second

Power output = 720 MW = 720 x 10^6 Watt

heat of combustion = 28 MJ/kg = 28 x 10^6 J/kg

Total heat given by coal = mass of coal x heat of combustion of coal

Heat input = 380 x 10^3 x 28 x 10^6 = 1064 x 10^10 J

Power input = Heat input / time = 1064 x 10^10 / 3600 = 2.956 x 10^9 Watt

Efficiency = Output power / Input power = (720 x 10^6) / (2.956 x 10^9)

Efficiency = 0.244 = 24.35 %

answer: the metamorphic rocks are formed when they are exposed to high pressure and high temperatures. this happens when one of the earth's plates comes in contact with the other plate by traveling in opposite directions, straight into each other or slipping under one another. the friction that is caused by this activity results in   melting of rocks and when it cools they are known as metamorphic rocks. this process needs a controlled amount of pressure and temperature otherwise it may turn into magma.