In diagram b, prove that the tension in the middle string is 3.3 n.
the mass=1kg
the force=10n

The tension in the middle string is 3.3 N

Explanation:

Two boxes move with same acceleration

The tension in the middle string is T

Lets start with the forces acting in the 2nd box

→ The tension T in the string in the direction of motion

Due to Newtons's Law

→ ∑ Force in direction of motion = mass × acceleration

→ T = M a

→ M = 1 kg

Substitute the value of M is the equation

→ T = a ⇒ (1)

The force acting on the 1st box

→ The force F in the direction of motion, and T in the string in opposite

   direction of motion

→ F - T = 2M a

→ F = 10 N , M = 1 kg

Substitute These values in the equation

→ 10 - T = 2(1) a

→ 10 - T = 2 a ⇒ (2)

Substitute equation (1) in (2)

→ 10 - T = 2 T

Add T to both sides

→ 10 = 3 T

Divide both sides by 3

→ T = 3.3 N

The tension in the middle string is 3.3 N

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 =