Kinematics equation for a free fall of height h
h=0*t+(1/2)gt^2
where g=9.80655 m/s^2 is acceleration due to gravity
Express equation in terms of t
t=sqrt(2h/g)
=sqrt(2*200/9.80655)
=20/sqrt(9.80655)
=6.3866 seconds
=6.387 seconds (to four significant figures)