The equation for force is F = ma. Solving for m yields the equation m = F/a.
In this case, m = 12000N/6.4m/s^2 = 1875 kg.
Lift is equal to drag, so if the drag was 12000N (newtons) the lift would be 12000N. it is mainly used for slowing the aircraft down for decend.
It is zero, since at constant velocity there is no acceleration. If 12000N are resisting motion, the truck is putting out 12000 N in opposite direction.
60 = 12000n Solving for the percent, we have: 60/12000 = n = 1/200 = .005 Multiplying by 100, you have 0.5%.