Question

A neutral metal bob is hanging on the bottom of a pendulum that is 15 cm long. A charged balloon is held near the metal bob and the pendulum is pulled up to a vertical angle of 20-deg. If the mass of the metal bob is 0.025kg, what is the charge on the balloon.

Answer 1

Step-by-step explanation:

See the figure attached

F is electrostatic force .

T cos20 = mg

T sin20 = F

Tan20 = F / mg

F = mg tan 20 = .025 x 9.8 tan20

= .09 N

Distance between bob and balloon

= 15 sin20 = 5.1 cm = .051 m

If q be the charge on balloon

F = 9 x 10⁹ x q² / .051²

= 3460 x 10⁹ q² = .09

q² = 26 x 10⁻⁶ x 10⁻⁹

q = 16.12 x 10⁻⁸ C .