Question

Two metal balls A and B of negligible radius are floating at rest on Space Station Freedom between two metal bulkheads, connected by a taut nonconducting thread of length 3.00 m. Ball A carries charge q, and ball B carries charge 2q. Each ball is 1.36 m away from a bulkhead.

(a) If the tension in the string is 2.55 N, what is the magnitude of q? (Ignore any contribution from induced charge in the bulkheads.)
μC

(b) What happens to the system as time passes? Explain. (Assume the thread is oriented perpendicular to the bulkheads.)

Answer 1

Two metal balls A and B of negligible radius are floating at rest on Space Station Freedom between two metal bulkheads, connected by a taut nonconducting thread of length 3m. Ball A carries charge q, and ball B carries charge 2q. Each ball is 1.36 m away from a bulkhead.
(a) If the tension in the string is 2.55 N, what is the magnitude of q?"

F = kQq / d²
2.55 N = 8.99e9N·m²/C² * q * 2q / (3)²
q = 3.57e-5 C = 35.7µC

"(b) What happens to the system as time passes? Explain."
I assume that over time the 2q charge will induce a negative charge in the bulkhead closest to it and will therefore eventually move toward that bulkhead. (That requires that we no longer "ignore any contribution from induced charge in the bulkheads." If we do continue to ignore, I'd say that nothing happens.)

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