Answer:
(a) The self inductance, L = 21.95 mH
(b) The energy stored, E = 4.84 J
(c) the time, t = 0.154 s
Explanation:
(a) Self inductance is calculated as;

where;
N is the number of turns = 1000 loops
μ is the permeability of free space = 4π x 10⁻⁷ H/m
l is the length of the inductor, = 45 cm = 0.45 m
A is the area of the inductor (given diameter = 10 cm = 0.1 m)

(b) The energy stored in the inductor when 21 A current ;

(c) time it can be turned off if the induced emf cannot exceed 3.0 V;

Answer:
Most of materia isnt life.
Explanation:
The living organisms (life) aren't the most abundant thing in universe.
Hydrogen and helium are present in everywhere, but life isn't.
There is no reason to think because we have a lot of a thing, the life must be made for this thing.
The organic life just can exists because some mysterious properties about carbon, that is the basic foundation of life, carbon is a special element, why? We don't know, actually, it's a huge problem for science discover why the carbon can makes life be possible and other elements can't. But we know is this element that makes life possible.
So, note there isn't relation about the quantity of a material in Universe and the life constituition. In addition, look around, organic materials are very rare in Universe, Earth is one in lots of places and in most of this places there isn't sign of life.
Even in Earth the life looks abundant, in Universe it isn't, the same way in Universe the Hydrogen and Helium are abudant, in Earth isn't soo.
When someone is struct by lightning, the electricity passes through the body, into the earth. Here, our body acts as a lightning conductor to complete the earthing process.
I assume that the ball is stationary (v=0) at point B, so its total energy is just potential energy, and it is equal to 7.35 J.
At point A, all this energy has converted into kinetic energy, which is:

And since K=7.35 J, we can find the velocity, v: