A drop of water of mass 18×10−6kg    falls away from the bottom of a charged conducting sphere ( 2.5×10−6 C ) of  radius 20cm carrying with it charge of  10−9 coulomb . What is the speed of the drop when it has fallen 30cm?ε0=14π×9×109                  g=9.8m/s2

From law of conservation of energy mechanical energy at A= Mechanical energy at BTake point B as reference point (zero gravitational potential energy),∴mg0.3+14πε0q1q20.2=0+12mv 2+   q1q24πε010.2+0.3                               Whre    m=18×10−6kg                                   q1=2.5×10−6c                                   q2=10−9c by solving  it   v=3.65  m/s