Answer:
4v/3
Explanation:
Assume elastic collision by the law of momentum conservation:

where v is the original speed of car 1, v1 is the final speed of car 1 and v2 is final speed of car 2. m1 and m2 are masses of car 1 and car 2, respectively
Substitute 

Divide both side by
, then multiply by 6 we have



So the final speed of the second car is 4/3 of the first car original speed
The power of is series combination is Vn^2 times that of a parallel combination.
For series combination :
Req = R + R + R + ............... n times = nR
I = Δv/nr
Power = (Δv/nr)^2 × nr = Δv^2/nr
For parallel combination
1/req = 1/R + 1/R + 1/R +................(n times) = n/R
Req = R/n
Power = Δv/(R/n) = nΔv^2/R
Ratio = Δv^2/nr/n·Δv^2/R = 1/n^2
Hence, power of is series combination is Vn^2 times that of a parallel.
Learn more about parallel combination here:
brainly.com/question/12400458
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The answer is definitely C.) their molecules move at the same average speed