Two cars $A$ and $B$ each of mass $10^3 \mathrm{~kg}$ are moving on parallel tracks separated by a d

Question

Two cars $A$ and $B$ each of mass $10^3 \mathrm{~kg}$ are moving on parallel tracks separated by a distance of 10 m , in same direction with speeds $72 \mathrm{~km} / \mathrm{h}$ and $36 \mathrm{~km} / \mathrm{h}$. The magnitude of angular momentum of $\operatorname{car} A$ with respect to car $B$ is $\_\_\_\_$ J.s.

Professor PC Thomas Classes · Answer

The speeds are $v_A = 72	ext{ km/h} = 20	ext{ m/s}$ and $v_B = 36	ext{ km/h} = 10	ext{ m/s}$. The relative velocity of car A with respect to car B is $v_{rel} = v_A - v_B = 20 - 10 = 10	ext{ m/s}$. The perpendicular distance between them is $r_\perp = 10	ext{ m}$. The magnitude of angular momentum is $L = m v_{rel} r_\perp = 10^3 	imes 10 	imes 10 = 10^5	ext{ J.s}$.