Refer to the diagram shown below.
m = 1.0 kg
Let R = resistive force of the water.
The boat accelerates from rest to 0.20 m/s in 0.50 s. Its acceleration is
a = (0.20 m/s)/(0.50 s) = 0.40 m/s²
The driving force on the boat is Fcos(45°) - R. Therefore
(2cos(45°) - R N) = (1 k)*(0.4 m/s²)
1.4142 - R = 0.4
R = 1.0142 N
Answer: The resistive force of the water is 1.0 N (nearest tenth)
