acceleration is the rate at which velocity changes; here we are told the speed increases by 9.8m/s for each second of travel
assuming the object starts at rest, the object has a speed of 9.8m/s after one second, and a speed of 19.6m/s after two
mathematically, we write
v= at
where v is the velocity, a is the acceleration and t is the time of travel
so v= at = 9.8m/s/s x 2s = 19.6m/s
