A pith-ball A of mass `9xx10^(-5)` kg carries a charge of `5 mu `C. What must be the magnitude and sign of the charge on a pith-ball B held 2 cm directly above the pith-ball A, such that the pith-ball A remains stationary ?

A free pith ball p of 10g carries of 5xx10^(-8) C . What must be the nature and maganitude fo charge that should be given to another pith ball Q fixed 7 cm below the former ball, so that upper ball is statinary ?

A free pith ball of mass 6g carries a positive charge of (1//3) xx 10^(-7) C . What is the nature and magnitude of charge that should be given to a second pith ball fixed 5 cm vertically below the former pith ball so that the upper pith ball is stationary.

A small ball of paper has mass 9xx10^(-5) kg and carries a charge of 5muC . When it is held over another charged ball of paper at a distance of 2cm above it, the two balls stay in equilibrium. What is the charge on the second hall ?

A positively charged glass rod is brought near an uncharged pith ball penduium. What happens to the pith ball ?

A ball of mass 2 xx 10^(-3) kg carries a charge of 2 xx 10^(-8) C. This ball is given an initial horizontal velocity of 5 xx 10^(4) ms^(-1) in the earth's gravitational field. What is the magnetic field required to keep the ball moving without deflection ? [Hint : F_(m) (magnetic force) =q_(0)vB "sin"theta=omegag ]

A metal ball of radius R = 1.5 cm has a charge q = 10 muC . Find the molecules of the vector fo the resultant force acting on a charge located on one half of the ball.

A sphercial ball of mass 5kg is resting on a plane with angle of inclination 30^(@) with respect to the horizontal as shown in the figure. The ball is held in place by a rope attached horizontally to the top of the ball and to the slope. The frictional force acting on the ball is