A 0.00275-kilogram air inflated balloon is given an excess negative charge, q1 =
ID: 1436599 • Letter: A
Question
A 0.00275-kilogram air inflated balloon is given an excess negative charge, q1 = -3.25 × 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 = 0.0740 m to make the balloon float. In order for this to occur, what polarity of charge must the rod possess? How much charge, q2, does the rod have? Assume the balloon and rod to be point charges. The Coulomb force constant is 1/(4 0) = 8.99 × 109 N·m2/C2 and the acceleration due to gravity g = 9.81 m/s2.
Explanation / Answer
Polarity of charge must the rod possess is positive.
If weight of the ballon is equal to attractive force between rod and ballon then the ballon is floated.
i.e., attractive force between rod and ballon = Weight of the ballon
Kqq' / d 2 = mg
From this charge of rod q ' = mgd 2 /Kq
Where K = Coulomb's constant = 8.99 x10 9 Nm 2/C 2
d = 0.074 m
q = charge of ballon = 3.25 x10 -8 C
m = mass of ballon = 0.00275 kg
Substitute values you get
q ' = (0.00275)(9.81)(0.074) 2/(8.99x10 9)(3.25x10 -8)
= 5.056 x10 -7 C
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