1. What is the efficiency of a heat engine that does 1250 J of work and gives off 5250 J of heat to the cold reservoir?

in pic

explanation: found it here http://gaaq.weebly.com/uploads/7/8/8/4/78844490/chapter_11_q_as.pdf

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.

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 =