An electron is fired from the right (to the left), directly at a smal plastic sp

Question

An electron is fired from the right (to the left), directly at a smal plastic sphere that has a total charge of -3.0 microcoulombs spread uniformly over its surface. The electron is fired from very far away and moves directly toward the center of the plastic sphere, which is held in place.

a) When the electron is 100.0 meters from the sphere, what is the electric field it experiences?

The electron slows down and eventually stops (momentarily) when it is 24 m from the center of the sphere.

b) What is the electric potential 24 m from the plastic sphere?

c) What was the original speed at which the electron was fired?

Explanation / Answer

a) Electric field due to sphere at 100m from sphere = KQ/R^2 = 9*10^9*3*10^(-6)/100^2 = 2.7 N/C to the left (ans)

b) Electric potential = KQ/R = 9*10^9*(-3)*10^(-6)/24 = -1125 V (ans)

c) Using energy conservation ,

eV = 1/2*m*V^2

1.6*10^(-19)*1125 = 1/2*9.109*10^(-31) *V^2

V = 2.01*10^7 m/sec (ans)

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