Objects in free fall accelerate due to a. gravity b. momentum c. energy d. velocity

The correct answer is A.

Objects in free fall accelerate due to gravity.

Explanation:

Momentum can help an object to keep its state of motion at a constant velocity when no external force is applied. It can never accelerate the object.

According to the laws of motion, we know that acceleration is produced in a body only when a Force is applied in the direction of motion of body.

During a free fall, only the force of gravity is acting on an object and that too in the direction of its motion. Hence, the acceleration produced in a free falling object is due to gravity.

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 =