Two cars moving in the same direction have speeds of 100 kmh−¹ and 130 kmh−¹. What is the velocity of the faster car as measured by an observer in the slower car?

A. 30 kmh−¹
B. 130 kmh−¹
C. 200 kmh−¹
D. 230 kmh−¹

Correct Answer:

Option A – 30 kmh−¹

Explanation

Since the cars are moving in the same direction, the velocity of a body A, Va, relative to another body B, Vb is given by V = Va – Vb
∴ the velocity of faster car is measured by the observer in the slower car is V = 130kmh¯¹ – 100 kmh¯¹ = 30 kmh−¹