We know the acceleration of his movement; he was falling under gravity and thus g=10m/s^2. The equation for the distance an object covers when it has constant acceleration g is given by: s=1/2*g*t^2. We know g and t in this equation (t=2 sec), so we just need to substitute. s=10*2*2/2=20 m. The distance is 20 m, and this is the height from which he jumped off.
