(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Two small metallic spheres, each of mass

0.14 g are suspended as pendulums by light

strings from a common point as shown. The

spheres are given the same electric charge, and

it is found that the two come to equilibrium

when each string is at an angle of 7◦ with the

vertical.

The value of Coulomb’s constant is

8.98755 × 109 N · m2/C2 and the acceleration

of gravity is 9.81 m/s2 .

If each string is 13.7 cm long, find the mag-

nitude of the charge on each sphere.

Answer in units of nC.

2. Relevant equations

y=Tcos(theta)=mg

x=Tsin(theta)=Fe

3. The attempt at a solution

Tcos(7)=(.14g)(9.81)

T=1.38371

1.38371sin(7)=.168632

q=sqrt((.1683632)(2*(.137sin7)^2))/8.98755x10^9

q=1.44639e-7

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# Homework Help: Electric forces

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