A child is stationary on a swing. The child is given a push by a parent and the child starts swinging.
The parent stops pushing the child
Figure 2 shows how the kinetic energy stored in the child varies over the first few swings
kinetic energy
time
Figure 2
Explain the energy changes during the first few swings

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 =