A. Calculate the potential energy of a system of two small spheres, one carrying

Question

A.

Calculate the potential energy of a system of two small spheres, one carrying a charge of 2.00C and the other a charge of -4.00C , with their centers separated by a distance of 0.210m . Assume zero potential energy when the charges are infinitely separated.

B.

Suppose that one of the spheres is held in place and the other sphere, which has a mass of 1.90g , is shot away from it. What minimum initial speed would the moving sphere need in order to escape completely from the attraction of the fixed sphere? (To escape, the moving sphere would have to reach a velocity of zero when it was infinitely distant from the fixed sphere.)

Explanation / Answer

Potential energy = k q / r

= [8.99 * 109 * 2.00 * 10-6 * (-4.00) * 10-6 ] / 0.210

= -0.342 J

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v = sqrt [ 2 k / m ]

= sqrt [ 2 * 0.342 / 1.9 * 10-3 ]

= 18.97 m/s

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