Two tiny spheres have the same mass and carry charges of the same magnitude. The

Question

Two tiny spheres have the same mass and carry charges of the same magnitude. The mass of each sphere is 6.78 10-6 kg. The gravitational force that each sphere exerts on the other is balanced by the electric force. (a) What algebraic signs can the charges have? opposite algebraic sign, one positive and one negative the same algebraic sign, both positive the same algebraic sign, both negative the same algebraic sign, both positive or both negative Correct: Your answer is correct. (b) Determine the charge magnitude.

Explanation / Answer

Your first thought is (hopefully) well wait, I'm not given their distance apart(which I'll call r)! That's crap! Usually when that happens the "missing" value in question finds its way out of the problem while doing the math, which is the advantage to working out a problem symbolically, solving it, and then plugging in numbers, then you know what you REALLY need so Fg=G*m1*m2/r^2 and Fe=C*q1*q2/r^2 What the problem tells us is they cancel out, so Fg=Fe G*m1*m2/r^2=C*q1*q2/r^2, and sure enough multiply both sides by r^2 G*m1*m2=C*q1*q2, and q1=q2 as told in the problem, so I'll just call it q, so G*m1*m2=C*q^2 You know G, m1 and m2(they're the same as well), and C, so just solve for q

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