Your sister wants to participate in the yearly science fair at her high school a

Question

Your sister wants to participate in the yearly science fair at her high school and asks you to suggest some exciting project. You suggest that she experiment with your recently created electron extractor to suspend her cat in the air. You tell her to buy a copper plate and bolt it to the ceiling in her room and then use your electron extractor to transfer electrons from the cat to the plate. If the cat weighs 7.4 kg and is suspended 1.1 m below the ceiling, how many electrons have to be extracted from the cat? Assume that the cat and the metal plate are point charges.

I keep getting the answer 8.52 e 14 electrons which is not right. I don't know what I am doing wrong.

Explanation / Answer

suppose charge q is extracted from cat.

then electric force = kq*q /h^2

balancing forces in vertical direction,

kq^2 / h^2 = mg

(9 x 10^9 x q^2 ) / 1.1^2 = 7.4 x 9.81

q = 9.88 x 10^-5 C

and ne = q

n = (9.88 x 10^-5) / (1.6 x 10^-19) = 6.17 x 10^14 electrons

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