Answer:
Some elements are reactive because the outermost energy levels of their atoms are only partially filled. Therefore, these atoms can easily gain or lose electrons to form ions. The atoms of nonreactive elements have filled outermost energy levels
Explanation:
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When two surfaces slide against each other, a force called friction makes them stick very slightly together. Smooth surfaces, like ice and glass, are easy to slide over. They create very little friction. Rough surfaces like rock and sand create much more friction, and are easy to grip on to.
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Here we can use momentum conservation as in this type of collision there is no external force on it

now here we can say




now here we can say


now by coefficient of restitution
for elastic collision we know that e = 1


now by solving the two equation


also we know that

so final speed of the nail is 6.875 m/s
Answer:
A)
B)
Explanation:
Given that
Force = F
Increase in Kinetic energy = 

we know that
Work done by all the forces =change in the kinetic energy
a)
Lets distance = d
We know work done by force F
W= F .d
F.d=ΔKE


b)
If the force become twice
F' = 2 F
F'.d=ΔKE'
2 F .d = ΔKE' ( F.d =Δ KE)
2ΔKE = ΔKE'

Therefore the final kinetic energy will become the twice if the force become twice.
To find the area, we just need to multiply the length by the width. 200 x 75 = 15,000. The mall has an area of 15,000 sq. feet.