John Jacob Jingleheimer Thompson got onto his rocket sied. After the sled was traveling at 9 m/s, he engaged the engines which accelerated the rocket at 15 m/s2. How fast was john moving after 7 seconds?

The drag force, fd, imposed by the surrounding air on a vehicle moving with velocity v is given by fd = cdaρv 2/2 where cd is a constant called the drag coefficient, a is the projected frontal area of the vehicle, and ρ is the air density. an automobile is moving at v = 80 kilometers per hour with cd = 0.28, a = 2.3 m2, and ρ = 1.2 kg/m3.