Gymnasts often practice on foam floors, which increase the collision time when a gymnast falls. what effect does this have on collisions?

the change in momentum needed to stop the gymnast is increased.

the change in momentum needed to stop the gymnast is decreased.

the force exerted by the floor on the gymnast decreases.

the force exerted by the floor on the gymnast increases

For some reason I can't comment on questions, so I'll just do it like this.

"The answer would be: " The force exerted by the floor on the gymnast decreases.  "

According to the impulse-momentum change theorem, Force and time are inversely proportional to each other. Given that, foam floors increase the collision time. As the quantity of impulse is kept the same, then an increase of time must indicated a decrease in force. "

I'd like to simplify it.

Basically, what he/she is saying, is that the longer the collision time, the less force is acted on the gymnast. Now, the reason for this, is because the same amount of force is acted on him, but less for longer. It's like lifting up a car that weighs 4000 pounds. You can't lift up 4000 pounds at once, but you can lift up 40 pounds 100 times pretty easily. That's why we use levers. It's similar here, you're having the same amount of force enacted on you, but it hurts far less, and has less of a chance of breaking bones.

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 =