Marble A has a mass of 0.25 kg and moves 1.0 m/s to the right. It strikes the identical marble, B, which is at rest. Four students predict what will happen after the collision.

Predicted Results after Collision

Marble A
Marble B

Speed
Direction
Speed
Direction
Student A
2.0 m/s
Left
2.0 m/s
Left
Student B
0 m/s
None
1.0 m/s
Right
Student C
1.0 m/s
Left
1.0 m/s
Right
Student D
2.0 m/s
Left
0 m/s
None

Which student’s prediction is most likely correct?
Student A
Student B
Student C
Student D

Student B

Explanation:

The conservation of momentum principle means the sum of the velocities of the two marbles cannot be greater than the initial velocity of marble A, since they are identical (most importantly, in terms of their mass).

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 =