Calculating Time for a Boat to Slow Down Using Friction and Kinematics

[Parth Dave]

A 1000 kg boat is traveling 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 a lot 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?

 

[Tide]

Does this help?

$$m\frac{dv}{dt} = -70v$$

 

[Parth Dave]

Never mind, i figured it out.

 

[Parth Dave]

Yes it did tide, but you were about 10 seconds to late :P.