The motorized toy boat experiences a net force of 0 N between 4 s and 8 s.
The motorized toy boat moves at 8 m/s (u) at 4 s and at 8 m/s (v) at 8 s. We can calculate the acceleration (a) in that period using the following kinematic expression.
The object with a mass (m) of 2.0 kg experiences an acceleration of 0 m/s². We can calculate the net force (F) in that period using Newton's second law of motion.
The motorized toy boat experiences a net force of 0 N between 4 s and 8 s.