A projectile of mass 0.1kg travelling horizontally through the air with speed v(t) experiences a drag force D(t) whose magnitude is given by: D(t)=0.001[v(t)]^2.
At one instant the projectile's speed is measured to be 100m/s. Calculate the speed of the projectile after a time of 3s has elapsed, during which the projectile continues to travel horizontally.