A student has chosen to study a swinging pendulum . The pendulum would bea. a system b. the surroundings c. a universe d. a force

To find:

What a pendulum is?

Explanation:

A system is a matter defined by the walls of space.

A surrounding is an environment around the system in observation.

A pendulum is a system containing the bob of the pendulum and the string to which the bob is attached.

The rest of the environment around the pendulum is considered as the surrounding.

Final

The pendulum the student has chosen to study is a system.

Thus the correct answer is option a.

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 =