C. a cello playing music at the concert
Answer:
The mass of the sand that will fall on the disk to decrease the is 0.3375 kg
Explanation:
Moment before = Moment after

where;
I is moment of inertia = Mr² = 0.3 x (0.3)² = 0.027 kg.m²
substitute this in the above equation;
![m = \frac{ 0.027[3(2 \pi) - 2(2 \pi)]} {0.2^2 * 6\pi } = \frac{ 0.027[6 \pi - 4\pi]} {0.2^2 * 4\pi }\\\\m = 0.3375kg](https://tex.z-dn.net/?f=m%20%3D%20%5Cfrac%7B%200.027%5B3%282%20%5Cpi%29%20%20-%202%282%20%5Cpi%29%5D%7D%20%7B0.2%5E2%20%2A%206%5Cpi%20%7D%20%3D%20%5Cfrac%7B%200.027%5B6%20%5Cpi%20%20-%204%5Cpi%5D%7D%20%7B0.2%5E2%20%2A%204%5Cpi%20%7D%5C%5C%5C%5Cm%20%3D%200.3375kg)
Therefore, the mass of the sand that will fall on the disk to decrease the is 0.3375 kg
A) initial volume
We can calculate the initial volume of the gas by using the ideal gas law:

where

is the initial pressure of the gas

is the initial volume of the gas

is the number of moles

is the gas constant

is the initial temperature of the gas
By re-arranging this equation, we can find

:

2) Now the gas cools down to a temperature of

while the pressure is kept constant:

, so we can use again the ideal gas law to find the new volume of the gas

3) In a process at constant pressure, the work done by the gas is equal to the product between the pressure and the difference of volume:

by using the data we found at point 1) and 2), we find

where the negative sign means the work is done by the surrounding on the gas.
Answer:

Explanation:
According to question,
Charge 1 and charge 2 are 
The distance between charges is 2 m
We need to find the force with which two positive charges repel. It is called electrostatic force of repulsion. It can be given by :

So, the electric force of repulsion is
.