A motor with an operating resistance of 24Ω is connected in a circuit witn 0.4A of current. The battery voltage must be volts

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The answer is a.  i hope this

Answer(a)   the matererials that are in contact, the two materials and the nature of their surfaces/// (b)/// the force pushing the two surfaces together, pushing the surfaces together causes the more of the asperities to come together and increases the surface area in contact with each other