Answer:
i would say the third one
Explanation:
may i be brainliest?
4. Intermediate conductivity and a low melting point.
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20m/s, honestly I have know idea what the asnwer is but if i had to guess, this would be my answer.
Answer:

Explanation:
From the question we are told that:
Frictional force 
Coefficient of kinetic friction 
Generally the equation for Normal for is mathematically given by

Therefore


That n2 = 2*n1. That is, the index of refraction is twice as big in medium 2 since v=c/n