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## Homework Statement

a) From a large distance away, a particle of mass 6 grams and charge 54 μc is fired at 25 m/s to the right straight toward a second particle, originally stationary but free to move, with mass 13 grams and charge 22 μc. Find the distance of closest approach between the charges.

b) Four identical particles each have charge of 4 μC and mass 2 grams. They are released from rest at the vertices of a square of side 42 cm. How fast is each particle moving when their distance from the center of the square triples?

## Homework Equations

a) ΔU + ΔK = 0

b) U=(kQ

_{1}Q

_{2})/r , ΔU + ΔK = 0, K = (1/2)mv

^{2}, V = (KQ)/r

## The Attempt at a Solution

a) not sure how to do this problem other than knowing that V

_{i}= 25 m/s for the 6 gram particle and V

_{i}= 0 for the 13 gram particle.