A motor-boat leaves a jetty, travels 4km upstream in 30min, immediately turns around and travels 4km downstream back to the jetty in 20min. The river channel is straight.
(a) Calculate the average speed for the entire round trip.
(b) Calculate the average velocity for the entire round trip.
(c) Suppose instead the boat stops 1km short of the jetty on its return journey while the total time still remains 50min. Calculate the new average speed and the new average velocity.
(d) Referring to your numerical results, explain how the net displacement influences the values of average speed and average velocity.