Final answer:
A boat can move upstream if it is rowed with a force greater than the stream's force in an upstream direction, as the force applied must overcome the opposing current.
Step-by-step explanation:
To answer the question, a boat can move upstream if it is rowed with a force C. greater than stream force in an upstream direction. When rowing a boat, the force that moves it forward is primarily the result of an interaction between the oars and the water the boat is traveling in. If you attempt to move upstream, you must overcome the force of the stream pushing against the boat. As the water near the shore moves slower due to resistance and turbulence, staying near the shore can minimize the force working against the boat when rowing upstream.
When considering velocities, the motion of a kayak is an example of the classical addition of velocities. As an object in motion, such as a kayak or boat, the total velocity is the vector sum of its velocity relative to the water plus the water's velocity relative to the riverbank. Therefore, to move upstream, the force applied by rowing must outmatch the downstream current.