If a boat and its riders have a mass of 1200 kg and the boat drifts in at 1.8 m/s how much work does sam do to stop it?

M = 1200 kg, the mass of the boat and its occupants
v = 1.8 m/s, the speed of the boat

The KE (kinetic energy) of the boat is
KE = (1/2)*m*v²
     = 0.5*(1200 kg)*(1.8 m/s)²
     = 1944 J

To stop the boat, the work done should be equal to the KE of the boat.
Therefore the work done is 1944 J.

  1944 J