Physics
Physics
Problem
A motor-boat is moving eastward on a calm river. At a certain instant, three horizontal forces act on the boat along the same straight line: • Thrust of the engine: towards the east • Water drag: towards the west • Steady wind force: towards the east (a) Calculate the magnitude and direction of the net horizontal force acting on the boat at this instant. (b) State the direction of the boat’s acceleration. (c) The engine is now shut off while the wind and water drag remain unchanged. Identify the new net force and predict the immediate change in the boat’s motion. Give reasons. (d) A little later the wind also drops to zero, leaving only the water drag acting on the boat. Describe the boat’s motion immediately after the wind stops, citing the principle involved.Intuitive explanation
This problem is about net force and Newton's second law — the key insight is that forces are vectors that add algebraically along a line, and the net force always determines both acceleration direction and how motion changes. Once you establish a consistent sign convention (east positive, west negative), you can combine all forces to find what actually happens to the boat, then predict how motion responds when forces change.
Intuitive explanation
This problem is about net force and Newton's second law — the key insight is that forces are vectors that add algebraically along a line, and the net force always determines both acceleration direction and how motion changes. Once you establish a consistent sign convention (east positive, west negative), you can combine all forces to find what actually happens to the boat, then predict how motion responds when forces change.