A certain kind of sounding instrument is sunk from a ship into the sea.According to thesounding requirements,it is necessary to determine the sinking depth y(from sea level)ofthe instrument and the sinking speed v as a function.Under the action of gravity,theinstrument sinks vertically from the rest of sea level,and is subjected to the action ofresistance and buoyancy in the process of sinking.Suppose that the mass of the instrumentis M,the volume is B,and the specific gravity of seawater is p.The resistance of theinstrument is proportional to the sinking speed,and the proportional coefficient is k(k>0),try to establish the differential equation satisfied by y and v,and find the functionrelation y y(v).