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A 0.00215-kilogram air inflated balloon is given an excess negative charge, q1 =

ID: 2002067 • Letter: A

Question

A 0.00215-kilogram air inflated balloon is given an excess negative charge, q1 = -3.75 × 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 = 0.0620 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. q2 is: positive, negative, proton, or neutral? q2=__________C

Explanation / Answer

The q can be calculated as :

q2 = Mass * g * d ^2 / (1/(4 0) * q1)

From the problem we know

Mass : 0.00215 Kg

g= 9.81

1/(4 0) = 8.99 * 10 ^9

q1 = -3.75 * 10 ^-8

q2 = [(0.00215*9.81){(0.0620)²}]*/(8.99*37.5) = 2.40*10 C or 240 nC