An experimental planetary lander of mass 120 kg120\text{ kg}120 kg is touchdown-tested on a simulated soil bed. At the moment of contact, the landing legs compress, taking 350 milliseconds350\text{ milliseconds}350 milliseconds to bring the lander to a complete stop. During this impact, the ground exerts an average upward force of 4800 N4800\text{ N}4800 N on the lander.
Calculate the downward velocity of the lander at the instant it first touched the soil bed. Show your working.