A small metal sphere, carrying a net charge of q1 = -2.1 microC , is held in a s

Question

A small metal sphere, carrying a net charge of q1 = -2.1 microC , is held in a stationary position by insulating supports. A second small metal sphere, with a net charge of q2 = -7.22 microC and mass 1.68g , is projected toward q1. When the two spheres are 0.800 m apart, q2 is moving toward q1 with speed 22.0 m/s . Assume that the two spheres can be treated as point charges. You can ignore the force of gravity. What is the speed of q2 when the spheres are 0.476m apart? How close does q2 get to q1?

Explanation / Answer

for the first part, we need to conserve energy to get the result.so,

kq1q2/x1 + KE1 = kq1q2/x2 + KE2

or 9*10^9*2.1*7.22*10^-12/0.8 + 0.5*1.68*10^-3*22^2 = 9*10^9*2.1*7.22*10^-12/0.476 + 0.5*1.68*10^-3*v^2

or v=18.59 m/s

b) let the distance be x.so,

9*10^9*2.1*7.22*10^-12/0.8 + 0.5*1.68*10^-3*22^2 = 9*10^9*2.1*7.22*10^-12/x

or x=0.236 m

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