At a steam power plant, steam engines work in pairs, the heat output of the first one being the approximate heat input of the second. the operating temperatures of the first are 750◦c and 440◦c respectively, and of the second 415◦c and 270◦c.

The rate at which coal burned is 111.12 kg/s.

Explanation:

Given that,

First initial temperature  =750°C

First final temperature =440°C

Second initial temperature  =415°C

Second final temperature =270°C

Suppose If the heat of combustion of coal is , at what rate must coal be burned if the plant is to put out 950 MW of power? Assume the efficiency of the engines is 65% of the Carnot efficiency.

The work done by first engine is

The work done by second engine is

Total out put of the plant is given by

Put the value into the formula

....(I)

We need to calculate the efficiency of first engine

Using formula of efficiency

We need to calculate the efficiency of second engine

Using formula of efficiency

Put the value of efficiency for first and second engine in the equation (I)

We need to calculate the rate at which coal burned

Using formula of rate

Hence, The rate at which coal burned is 111.12 kg/s.

it is given that trillions of microbes make up to 1% to 3% of the body mass.

let's take average of this percentage: 2%

consider the average mass of the human body as 70 kg.

then, trillions of microbes would have mass  

therefore, 100 trillion micro-organisms would weigh:

this is an approximate value and could change depending on the mass of the human body and percentage of the microbes present in it.

average mass per microorganism =