A1500 kg car traveling at 8 m/s slows to a stop when the driver hits the brakes. if the braking force between the tires and the road is a consistent 4200 n, then how long will it take for the car to stop?

First you fond the total force the car initialy has which is F=ma so it is 1500 times 8 which leads you to get 12000N then you divide the force of the car by the breaks and the road (4200N) which gives you 2.85 seconds for the car to come to a stop.

a.   mass number from atomic number

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 =