An electrically neutral model airplane is flying in a horizontal circle on a 2.5-m guideline, which is nearly parallel to the ground. The line breaks when the kinetic energy of the plane is 50 J. Reconsider the same situation, except that now there is a point charge of +q on the plane and a point charge of -q at the other end of the guideline. In this case, the line breaks when the kinetic energy of the plane is 52.6 J. Find the magnitude of the charges.
q=_____________C
Suppose the centripetal force in case 1 is Fcmax
Fcmax = mv12 / 2 , KEmax = mv12 / r
The centripetal force in case 2 is Fc' = Fc + Fq where Fq is the extra force by the charges.
Now, at the breaking point, Fcmax + Fq = mv1' 2 / r
Hence, KE'max - KEmax = m(v1' 2 - v12) / 2 = 2.6 J
and Fq = m(v1' 2 - v12) / r
=> kq2 / r2 = m(v1' 2 - v12) / r
=> q2 = mr(v1' 2 - v12) / k = 2(KE' - KE)r / k = 5.2(2.5)/(9*109) = 14.44*10-8
=> q = 3.8 * 10-4C
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