Three travelers move along the same straight east–west road on a clear day
PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
Three travelers move along the same straight east–west road on a clear day.
• Car A moves east at a constant speed of 20 m/s.
• Car B moves east at a constant speed of 10 m/s.
• A cyclist pedals west at a constant speed of 5 m/s.
Throughout the trip, each traveler makes visual observations of the others without using any measuring instruments.
(a) Rank, from greatest to least, the magnitude of the velocity of Car A as measured by the following observers. If two observers would measure the same magnitude, state that explicitly.
(1) A person standing on the ground beside the road
(2) The driver of Car B
(3) The cyclist
(b) Provide a qualitative explanation for your ranking in part (a). In your discussion, clearly describe how the choice of observer affects the measured magnitude and direction of Car A’s velocity, and why no numerical calculation is required to establish the ordering.