# A 5*10^-2 kg mass with a charge of +0.75*10^-6 C is hung by a thin insulated thread.  A charge of -0.9*10^-6 C is held 0.15 meters directly to the right so that the thread makes an angle q with...

A 5*10^-2 kg mass with a charge of +0.75*10^-6 C is hung by a thin insulated thread.  A charge of -0.9*10^-6 C is held 0.15 meters directly to the right so that the thread makes an angle q with the vertical.  What is the angle q and the tension in the string?

justaguide | College Teacher | (Level 2) Distinguished Educator

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A 5*10^-2 kg mass with a charge of +0.75*10^-6 C is hung by a thin insulated thread.  A charge of -0.9*10^-6 C is held 0.15 meters directly to the right so that the thread makes an angle q with the vertical.

There are two forces acting on the 5*10^-2 kg mass. One is the gravitational force of attraction equal to m*g = 5*10^-2*9.8 = 0.49 N acting vertically downwards and the other is a force exerted by the oppositely charged particle held 0.15 m away.

The horizontal force given by Coulomb's Law is equal to 8.987*10^9*0.75*10^-6*0.9*10^-6/0.15^2 N

= 0.26961 N

Due to the two forces the thread from which the mass is suspended makes an angle q with the vertical equal to arc tan (0.26961/0.49) = 28.82 degrees.

The tension in the string is sqrt( 0.49^2 + 0.26961^2) = 0.5592 N

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