The relationship between the mass m of a material, its volume v, and its density d isa. v= mdb. vm=dc. dv=md. d+v=m

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 =

490 n

f=125n a=2.5m/s2