A $2\mathrm{.}3$ mmmm $-$diameter sphere is charged to $-4\mathrm{.}6$ nCnC $.$ An electron fired directly at the sphere from far away comes to within $0\mathrm{.}35$ mmmm of the surface of the target before being reflected.

Part A

What was the electron's initial speed?

Express your answer in meters per second.

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vinitialvinitial $=$

nothing

m$/$sm$/$s

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Part B

At what distance from the surface of the sphere is the electron's speed half of its initial value?

Express your answer in meters.

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dd $=$

nothing

mm

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Part C

What is the acceleration of the electron at its turning point?