Copper, gold and silver are three of them.
'N' is labelled 'runoff'. That's when the water is down. Streets are wet, worms come out of the ground, and water flows down the street to the sewer.
You first find the mass and the volume of that object. Then you divide mass ÷ volume
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.
Here we can say that there is no external torque on this system
So here we can say that angular momentum is conserved
so here we will have

now we have



similarly let the final distance is "r"
so now we have


now from above equation we have


so final distance is 0.04 m between them