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A 0.00275-kilogram air inflated balloon is given an excess negative charge, q_1

ID: 2002007 • Letter: A

Question

A 0.00275-kilogram air inflated balloon is given an excess negative charge, q_1 = -4.00 times 10^-8 C, by rubbing it with a blanket. It is found that a charged rod can be held above the balloon at a distance of d = 0.0800 m to make the balloon float. In order for this to occur, what polarity of charge must the rod possess? How much charge, q_2, does the rod have? Assume the balloon and rod to be point charges. The Coulomb force constant is 1/(4pi e _0) = 8.99 times 10^9 N m^2/C^2 and the acceleration due to gravity g = 9.81 m/s^2.

Explanation / Answer

a)

Positive ,Since opposite charges attrat each other ,so for rod to hold the ballon up against its weight ,the ballon is given negatively charged and therefore rod must be positively charged.

b)

Force of attraction between 2 charges = Weight of the ballon

K|Q1||Q2|/d2=mg

(8.99*109)(4*10-8)*Q2/0.082 = 0.00275*9.81

Q2=4.8*10-7C