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## Homework Statement

A 1000 kg boat is traveling at 100km/h when its engine is shut off.The magnitude of the frictional force ## \vec f_k## between boat and the 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

## Homework Equations

## \vec F=m \vec a##

##v-v_0=at##

## The Attempt at a Solution

I turned km/h to m/s which its ##100km/h=27.7 m/s## and ##45km/h=12.5m/s##

then ;

##ma=-70v##

here the connfusing part is ##a## decreases when v decreases.Theres no constant decelaration.I thought integral but without distance I stucked.

##∫mdv=∫-70vdt##

I don't know what to do.

Thank you