As radiation enters a solid or liquid, the light waves are absorbed and reflected by the atoms. the resulting reflection from an atom can be in any direction and is random. you can understand opacity in terms of the scattering of radiation. The more opaque, the more scattering. 
(The truth is far more complicated than this, check out Richard Feynmans lectures on "Quantum Electro Dynamics" to learn the reality of it. )
        
             
        
        
        
Answer:
2k
Explanation:
100W X 10h = 1000Wh = 1KWh thus cost is 2k
 
        
             
        
        
        
Explanation:
KE = 1/2*m*v^2
mass won't change
but velocity is
A: the force is pushing against the direction of the object, so velocity is decreasing, so KE is decreasing
B: the F net line is pretty much straight up, which means there is no net force pushing to the left, but velocity is still increasing
Why? Because if you use the pythagorean theorem, the hypotenuse is always longer than the legs.
Note: velocity only ever stays the same if there is no net force (or 0 acceleration), so all four of these are either decreasing or increasing
C: there is a net force to the right, so velocity is increasing
D: There is a net force to the right but velocity is to the left, so velocity is decreasing
Hope I got these right
 
        
             
        
        
        
120/60= 2m per s
220/55= 4m per s
720/80= 9m per s 
Fastest run: 3rd run
Speed: 9m per s
Slowest: 1st run
Speed: 2m per s