A ship is traveling at constant speed, i.e. the engine exerts a force equal to the drag force acting on the ship (right?). A cargo box is standing on the deck of the ship and is secured with a rope to the mast (see pic). When the ship kills the engine, the drag will create a sudden change in velocity, which (given that the ship's initial velocity is high enough) causes the box to continue moving relative to the ship and there will be a tug on the rope. How do I calculate the force acting on the rope? I figure that I can't use the same calculation as with a collision, since the deceleration is created by the ship's drag, which means that the deceleration won't be uniform. I already know the drag of the ship, it's speed and the mass of the box.