1. A 1000kg boat is traveling across a lake when its engine is shut off. The magnitude of the frictional force between the water and the boat is proportional to the boat's speed (proportionality constant is 70) . Find the time it takes the boat to slow to one half its speed when the engine was shut off. 2.Using Newton's second law: F=ma 3. I'm guessing the acceleration is not constant in this problem. So the constant acceleration equations don't apply. I don't know how to include the time in this problem if i have no equations to solve them in. Thanx in advance.