# Homework Help: Electron Escape Speed

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1. Dec 3, 2017

### mitchy16

1. The problem statement, all variables and given/known data
What is the escape speed of an electron launched from the surface of a 1.0-cm-diameter glass sphere that has been charged to 10nC?

2. Relevant equations
Given:
d= 1.0cm
r= 0.05cm= 0.0005m
q1 = 10nC = 10 x 10-9 (sphere)
q2 = -1.6 x 10-19 (electron)

Equation:
U = (kq1q2)/r
KE= ½mv2
3. The attempt at a solution
So, if the sum of kinetic and potential energy is supposed to be zero, then I get:

KE + U = 0
½me(ve)2 + (kq1q2)/r = 0
½(9.11 x 10-31)(v)2 + ( (8.99 x 109) (10 x 10-9) (-1.6 x 10-19) ) / (0.0005) = 0

If I solve the above equation^^, I get ve= 2.5 x 108 m/s, which is incorrect. The correct answer is 8.0 x 107 m/s. I am not sure what I am doing incorrectly, any help is appreciated. Sorry about the mess, I can't seem to figure out how to use TeX!

2. Dec 3, 2017

### Delta²

Your mistake is in the radius of the glass sphere Its 0.5cm=0.005m!

3. Dec 3, 2017

### mitchy16

Thank you, can't believe I didn't catch that. I re-did and got the correct answer!!