Answer:
it's all around you and it can't be destroyed
(3) The frictional force exerted by the floor on the box
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.
The tactile system is actually made up of two distinct skin senses;
protective and the discriminative system. The function of the protective system
is to alert us to harmful stimuli. The receptors of the system are the hairs of
our skin, head and genitals. The discriminative system is to show us what we
are touching, where on our bodies is touching us and what are touching us. The receptors
for his system are the hands, fingers, soles of feet and mouth and tongue.