Force = mass * acceleration. Acceleration = deltaV/deltaT, where deltaV is change in velocity, and deltaT is change in time. Deltav = final Velocity because initial velocity is 0. (Final Velocity)^2 = (initial velocity)^2 + 2ad, where a is gravity acceleration of 9.8m/s^2, and d is the height. Final velocity = sqrt(2*9.8*h) = sqrt(19.6h). Therefore, Force = m*sqrt(19.6h)/deltaT.
