Question

7. -11 points SerPSE9 23.P.077. My Notes Three identical point charges, each of mass m 0.100 kg, hang from three strings, as shown in the figure below. If the lengths of the left and right strings are each L-20.0 cm, and if the angle θ is 45°, determine the value of q. 1M Need Help? Road t

Answer 1

the middle string is of such a length as to have all three charges on a horizontal line --

L = 20cm * cos45º = 14.14 cm

Then the force on either outer charge is

F = Σ kQ²/d² = Q² * 8.99e9N·m²/C² * (1/(0.1414m)² + 1/(2*0.1414m)²) = Q² * 5.619e11N/C²

Since the string is at 45º, this is equal to the weight:

W = mg = 0.100kg * 9.8m/s² = 0.98 N

so Q² = 0.98N / 5.619e11N/C² = 1.744e-12 C²

Q = 1.32e-6 C