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:
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Explanation:
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3 times 6= 18. The average speed is 19 mph.
hope this helps!
Answer:
F(Mars) = 2 G m M / (4 R)^2 force of Sun on Mars
F(Merc) = G m M / R^2 force of force of Sun on Mercury
R = distance of Sun from Mercury, m = mass of Mercury
F(Merc) / F(Mars) = 4^2 / 2 = 8