Which of the following systems has constant kinetic and potential energies? a car moving along a level road at constant speed
a car moving up a hill at constant speed
a car moving down a hill at constant speed
all of the above

A car moving along a level road at constant speed

The boat's velocity relative to the riverbank can be resolved into two components. the component going north is 2.7 m/s and the component going west is 1.2 m/s.we add these two vectors and then find the magnitude of the resultant to get the speed.the magnitude of the resultant vector from adding can be obtained by the pythagorean theorem.    to two significant figures, the boat's speed relative to the riverbank is 3.0 m/s.