Two cars A and B are travelling in the same direction with velocities v1 and v2 (v1 > v2). When the car A is at a distance d ahead of the car B, the. driver of the car A applied the brake producing a uniform retardation a. There will be no collision when

Initial relative velocity = v1 - v2,  final relative velocity = 0From            v2=u2-2as⇒0=v1-v22-2×a×s⇒               s=v1-v222aIf the distance between two cars is s, then collision will take place. To avoid collision d > s∴                             d>v1-v222awhere, d = actual initial distance between two cars.