Question

A $1800-kg$ car is stopped at a traffic light is struck from the rear by a $900-kg$ car. The two cars become entangled, moving along the same path as that of the originally moving car . If the smaller car was moving at $20m/s$ before the collision. What is the velocity of the entangled cars after the collision?

Answer 1

Momentum is conserved.

$M_{car1}{v}_1+M_{car2}{v}_2=(M_{car1}+M_{car2})\times v_3$

$1800\times 0+900\times 20=(1800+900)\times v_3$

$v_3=\frac{18000}{2700}=6.67m/s$