JAMB Physics 2010 Paper

Concept:Relative velocity for two objects moving in the same direction is the difference of their speeds.Explanation:Let the slower car speed be $v_s = 100\ \mathrm{kmh}^{-1}$.Let the faster car speed be $v_f = 130\ \mathrm{kmh}^{-1}$.Since both cars move in the same direction, the velocity of the faster car as seen by an observer in the slower car is:$v = v_f - v_s$$v = 130 - 100$$v = 30\ \mathrm{kmh}^{-1}$The direction is the same as the cars' motion.Answer:$30\ \mathrm{kmh}^{-1}$ (Option A).