A bob as cliating on a pendulum the maximum height of a bob is 20cm from the equilibrium position. calculate the velocitu of abob as it passes the equilibrium position ? g=10m/s² pleas formula

The answer is 4f======since electrostatic force is given by    we let f be the electrostatic force when  r = 1 m    if we let  denote the electrostatic force when the distance is decreased so that r = 0.5m, then    we established earlier that f = kq₁q₂. therefore    the force will now be 4f.