1. The problem statement, all variables and given/known data A boat, whose mass is m, is traveling at a speed of v_i when its engine is shut off. The magnitude of the friction force f between boat and water is proportional to the speed v of the boat: f=kv. Find the time t for the boat to slow down to speed v_f 2. Relevant equations 3. The attempt at a solution I think there should be some transformations with the help of calculus, but I really don't have any ideas.