Correct answer is D.
Explanation:
A) is not correct answer because this type of theory can not become law. Laws are properties that are same in any part of universe. Nebular theory is not correct for every part of universe.
B) is not correct answer because this theory could be replaced if some evidence show that some other theory is more likely to be correct.
C) is not correct answer because the study has been done on other nebulas in our galaxy. There are many nebulas and by obserwing them this theory was developed.
Answer:

Explanation:
Hello!
In this case, for this melting process, we can identify two sub-processes in order to take the stainless steel from solid to liquid:
1. Heat up from 298.15 K to 1673 K.
2. Undergo the phase transition.
Both process have an associated enthalpy as shown below:


Therefore, the required heat is:

Notice the problem is not providing neither the mass or volume, that is why we assumed the mass is 1 g; however, it can be changed to the mass you are given.
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Answer:
84.4 %
Explanation:
Mechanical efficiency = output work/input work × 100 %
output work = 432 J of work for the bike to turn the gears
input work = 512 J of work to ride.
Mechanical efficiency = 432 J/512 J × 100 %
= 0.844 × 100%
= 84.4 %
Answer:
805.48N/m
Explanation:
According to Hookes law
F = Ke
F is the force = mg
F = 2.4×9.8 = 23.52N
e is the extension = 2.92cm = 0.0292m
Force constant K = F/e
K = 23.52/0.0292
K = 805.48N/m
Hence the force constant of the spring is 805.48N/m