Calculating Time for 1000kg Boat to Slow from 90km/h to 45km/h

[Fallinleave]

A 1000kg boat is traveling at 90km/h when its engine is shut off. The magnitude of frictional force f_k between boat and water is proportional to the speed v of the boar: 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 45km/h.

The question does not ask for acceleration, so do I need to find the acceleration before finding the time?

In addition, Does anyone knows how to use a math template for posting this type of question?

Thanks,

 

[Fallinleave]

Any thought on it would be fine, thanks.

 

[ehild]

Use Newton's second law to get the relation between velocity v and acceleration, dv/dt. Solve the differential equation.

ehild