Hey everyone, I don\'t understand the following question. I know the answer to (

Question

Hey everyone,

I don't understand the following question. I know the answer to (b)is 1.89s, but I don't understand why. Could someone please explainthis for me? I will rate lifesaver for someone who would explainthis. Thanks!

A small metal ball (A) of mass 20 g carrying a charge +0.07µC is electrically insulated from a light vertical springthat supports it in equilibrium 12 cm above an insulatingplatform. An identical metal ball (B) is given a charge–0.07 µC and attached to the platform, directly underball A. A’s new equilibrium position is 10 cm above B.Now the platform is slowly raised until the balls come intocontact. After contact B is removed (a) Explain what happensand (b) what is the period of oscillation of ball A?

Explanation / Answer

The electrical force between the balls at equilibriumis   F = K Q2 / .12 F = 9 * 10E-9 * (7 * 10E-8)2 / .01 = 4.41 * 10E-3N This force is causing a spring extension of  F = k x Thus k = 4.41 * 10E-3 / .02 = .2205 The period of oscillation is   T = 2 (m / k) = 2 (.02 / .2205) = 1.89 After the charged balls come into contact the charge isneutralized and there is no an electrical force between the balls and the upper ball is free tooscillate at its natural frequency in SHM. F = 9 * 10E-9 * (7 * 10E-8)2 / .01 = 4.41 * 10E-3N This force is causing a spring extension of  F = k x Thus k = 4.41 * 10E-3 / .02 = .2205 The period of oscillation is   T = 2 (m / k) = 2 (.02 / .2205) = 1.89 After the charged balls come into contact the charge isneutralized and there is no an electrical force between the balls and the upper ball is free tooscillate at its natural frequency in SHM.

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