a) A 0.00200-kilogram air inflated balloon is given an excess negative charge, q
ID: 1593625 • Letter: A
Question
a)
A 0.00200-kilogram air inflated balloon is given an excess negative charge, q1 = -3.00 × 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 = 0.0760 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.
b)
As a laudably skeptical physics student, you want to test Coulomb's law. For this purpose you set up a measurement in which a proton and an electron are situated 979 nm from each other and you study the forces that the particles exert on each other. As expected, the predictions of Coulomb's law are well confirmed. You find that the forces are
Explanation / Answer
It has to be an attractive force, which means opposite charges, so the rod has to have a + charge.
Coulomb's law, force of attraction/repulsion
F = kQQ/r²
Q and Q are the charges in coulombs
F is force in newtons
r is separation in meters
k = 8.99e9 Nm²/C²
0.00200*9.81 = [{8.99*(10)*3.00*(10)*q}/{(0.0760)²}] or
q = [(0.00200*9.81){(0.0760)²}]*/(8.99*30) = 4.20*10 C or 420 nC
2) F = kQq / d² = 8.99e9N·m²/C² * (1.602e-19C)² / (979e-9m)² = 2.04e-16 N
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