Answer:
Time taken by A and B is 1.2 hr.
Explanation:
Given that
Time taken by tank when all(A+B+C) are open = 1 hr
Time taken by tank when A+C are open = 1.5 hr
Time taken by tank when B+C are open = 2 hr
If we treat as filling of tank is a work then
Work = time x rate
Lets take work is 1 unit
1 = 1(1/a+1/b+1/c) ---------1
1 = 1.5(1/a+1/c) ----------2
1 = 2(1/b+1/c) --------3
From equation 1 and 3
1=1(1/a+1/2)
a=2
Form equation 2
1 = 1.5(1/2+1/c)
c=6
From equation 3
1 = 2(1/b+1/6)
b=3
So time taken by
A is alone to fill tank is 2 hr
B is alone to fill tank is 3 hr
C is alone to fill tank is 6 hr
So 
Time taken by A and B is 1.2 hr.
If you want to change the thermos into an open energy system, you have to remove the lid. Once the lid is removed, the energy is no longer contained inside the thermos bottle. From the bottle, the energy dissipates to the environment.
<span>fluid friction of the air also known as drag</span>
To solve this problem we will apply the concepts of linear mass density, and the expression of the wavelength with which we can find the frequency of the string. With these values it will be possible to find the voltage value. Later we will apply concepts related to harmonic waves in order to find the fundamental frequency.
The linear mass density is given as,



The expression for the wavelength of the standing wave for the second overtone is

Replacing we have


The frequency of the sound wave is



Now the velocity of the wave would be



The expression that relates the velocity of the wave, tension on the string and linear mass density is





The tension in the string is 547N
PART B) The relation between the fundamental frequency and the
harmonic frequency is

Overtone is the resonant frequency above the fundamental frequency. The second overtone is the second resonant frequency after the fundamental frequency. Therefore

Then,

Rearranging to find the fundamental frequency


