I need help in Physics! Urgent!?

Destiny

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Question: an electron orbits a stationary proton at a distance of 5.29 x10^ -11. What is the kinetic energy of the electron?

Textbook answer: centripetal force =electric force.
mv^2 /r = QQ / (4pie Eo r^2)

Therefore 1/2 mv^2 = QQ/ (8pie Eo r)
Hnece K.E= -4.35 X 10^ -18 J

My question: How come gravitional force is not included since there is always a gravitonal force between two attractive particles orbiting each other. My take is that centripetal force = electric force + gravtional force. Is the textbook answer wrong OR is it because the mass of electron is too light and hence gravitional force is omitted?
 
Gravitational force is 37 magnitudes weaker than the electromagnetic force, so it doesn't contribute anything worthwhile here.
 
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