B is the answer because it causes impact and collides together.
To solve this problem we will apply Ohm's law. The law establishes that the potential difference V that we apply between the ends of a given conductor is proportional to the intensity of the current I flowing through the said conductor. Ohm completed the law by introducing the notion of electrical resistance R. Mathematically it can be described as

Our values are


Replacing,



Therefore the smallest resistance you can measure is 
<span>b. The coefficient of static friction for all contacting surfaces is μs=0.35. neglect friction at the rollers.
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We cannot answer the question if we do not have the answers - sorry!!