Hi, new member here ^_^ "A 1000kg boat is traveling at 90km/h when its engine is shut off. The magnitude of the frictional force f_k between boat and water is proportional to the speed v of the boat: f_k = 70v, where v is in meters per second and f_k is in newtons. Find the time required for the boat to slow to 45 km/h." From what I'm getting, the only force on the boat is the force of kinetic friction and as time passes the velocity decreases, so the force of kinetic friction's magnitude will decrease as well. So this will decrease the magnitude of the acceleration and cause velocity to decrease more slowly as time passes by ... I'm having trouble putting all that together not being used to dealing with non-constant acceleration problems so could someone please help me organize my thoughts for this problem? Thanks!