1. A race car moves along a circular track of radius 100m at a velocity of 25m/s. (a) What is the time taken to complete one lap of the circular track. (b) What is the time taken for 10
laps.

Given :

A race car moves along a circular track of radius 100m at a velocity of 25m/s.

To Find :

(a) What is  the time taken to complete one lap of the circular track.

(b) What is the time taken for 10  laps.

Solution :

Circumference of circular track,

a) Time taken to complete one lap is :

b) Time taken to complete 10 laps is :

Hence, this is the required solution.

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 =

3. dark matter

empty space could also be a simple vacuum