What is the force (in Newtons) between two positive particles each with a charge of 3.0 C and 5.0 m apart from each other

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current

How are period and frequency related to each other? dperiod is the reciprocal of frequency.

There was no intial y-momentum so the net final y-momentum must also be 0. they can have final velocities in the y-direction

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