Physics, 15.12.2020 22:50 dondre54

A pendulum swings back and forth. Is there energy in the system?

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Answer from: terrasami3152

yes

Explanation:

A pendulum should be able to contain enough energy to constantly be moving

Answer from: Quest

force is based upon mass and acceleration.the statement is not always true.

it can be explained from newton's second law of motion.

as per newton's second law of motion the rate of change of momentum is directly proportional to the applied force and takes place along the direction of force.

mathematically it can be written as -

$f\alpha \frac{dp}{dt}$

⇒ $f= k \frac{dp}{dt}$

here k is the proportionality constant whose value is 1.

$f=\frac{dp}{dt}$

$f= \frac{d[mv]}{dt}$

$f= m\frac{dv}{dt} +v\frac{dm}{dt}$

$f=ma+v\frac{dm}{dt}$ [a is the acceleration=dv/dt]

hence we see that force not only depends on mass and acceleration but also on velocity and rate of change of mass. force f will depend on mass and acceleration only when mass is constant.

hence the statement that force is based upon mass and acceleration is false.

Answer from: Quest

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 $= 2\%\hspace{1mm}of \hspace{1mm} 70\hspace{1mm} kg=\frac {2}{100}\times 70 =1.4\hspace{1mm} kg$

therefore, 100 trillion micro-organisms would weigh:

$\rightarrow 100\times1.4 kg = 140 kg$

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 = $\frac{1.4 kg}{10^12}=1.4\times10^{-12} kg$

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