A baseball is thrown vertically downward from the top of a 155 m tower with an initial velocity of -25 m/s. How long will it take, until it reaches the ground?

t = 2.55 s

Explanation:

Given that,

Height from which the baseball is thrown, h = 155 m

Initial velocity of the baseball, u = -25 m/s

We need to find the time taken by it to reach the ground. Let the time is t. Using equation of kinematics to find it as follows:

So, it will take 2.55 seconds to reach the ground.

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 =

answer: the potential energy decreases from 379 j to 243 j

explanation:

for the law of conservation of energy, the total energy in a system must be conserved. the total energy of the system is given by the sum of kinetic (k) and potential (u) energy:

e = k + u

the total energy is e=675 j, and this does not change.

initially, the kinetic energy is k=296 j, so the potential energy is

at the end, the kinetic energy is k=432 j, so the potential energy is

so, we see that the potential energy has decreased from 379 j to 243 j.