A point charge +Q=4.0μC is fixed to the ground. A tiny polystyrene sphere of mass m=4.5×10−6kg is released from rest a distance r=8.0cm directly above the fixed charge along the vertical line through Q.
Throughout this problem, take g=9.8ms−2 and assume no other forces act on the sphere besides gravity and the electrostatic interaction with Q.
(a) Determine the magnitude and sign of the charge q that the sphere must carry so that it remains at rest when released from that position.
(b) Suppose instead that the sphere carries a charge whose magnitude is twice the value you found in part (a), retaining the same sign. Immediately after release, calculate the magnitude and direction of its acceleration.