A 1000 kg boat is travelling at 90 km/h when its engine is shut off. The magnitude of the frictional force, fk, between boat and water is proportional to the speed, v, of the boat: fk = 70v, where v is in meters per second and fk is in newtons. Find the time required for the boat to slow to 45 hm/h. Now, I have absolutely no clue as to what to do. I've tried alot of different things and they have all led absolutely nowhere. I do know however that the a = 0.07v. Thats about all i can say for sure . Could someone nudge me in the right direction?