Physics
Physics
Problem
A ferry travels straight along an east–west river. When its engines are set to produce a speed eastward relative to the water, a passenger strolls westward relative to the deck. An observer on the riverbank measures the passenger’s motion and reports that the passenger is moving east relative to the ground. Assume all motion is strictly one-dimensional along the east–west line. (a) Calculate the speed and direction of the river’s current relative to the ground. (b) Determine the passenger’s speed relative to the water. (c) If the captain wants the passenger to appear motionless to someone on the shore, at what speed and in which direction should the passenger walk on the deck? Express your answer relative to the deck.Intuitive explanation
This is a relative velocity problem where you need to track motion through multiple reference frames. The key insight is that the passenger's velocity relative to the ground comes from combining two velocities: the ferry's motion relative to the water, and the passenger's motion relative to the ferry—but you must account for the river current, which is the "missing piece" that makes the ground frame different from the water frame. Work backwards from the ground observation to find the current's speed and direction.
Intuitive explanation
This is a relative velocity problem where you need to track motion through multiple reference frames. The key insight is that the passenger's velocity relative to the ground comes from combining two velocities: the ferry's motion relative to the water, and the passenger's motion relative to the ferry—but you must account for the river current, which is the "missing piece" that makes the ground frame different from the water frame. Work backwards from the ground observation to find the current's speed and direction.