A 62-kg boy on a 1.5-kg skateboard is moving at 1.2 m/s. The boy steps off the skateboard (Hint: this part is the collision- one thing separating into 2 things is an explosion collision) and now has a velocity of 1.1 m/s. How fast does the skateboard move after he steps off of it?

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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 =