Homework Help: physics

Posted by stoic-rider77 on Friday, January 18, 2013 at 9:34pm.

Two small plastic balls hang from threads of negligible mass. Each ball has a mass of 0.14g and a charge of magnitude q. the balls are attracted to each other. When in equilibrium, the balls are separated by a distance of 2.05cm and the threads attached to the balls make an angle of 20 degrees with the vertical.

Find:
a. The magnitude of the electric force acting on each ball.
b. The tension in each of the threads.
c. The magnitude of the charge on the balls.

physics - Elena, Saturday, January 19, 2013 at 6:10am
r=0.0205 m
α=20⁰,
m = 0.00014 kg=1.4•10⁻ ⁴ kg•

F(el)=kq₁•q₂/r²=kq²/r²,

T•sin α =F(el)= kq²/r²,
T•cosα=mg .
T•sin α/ T•cosα= kq²/r²mg,
tanα = kq²/r²mg,
q=sqrt{ r²•m•g•tan α/k}= ...

T= mg/cos α = ….

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