The rockets would need to accelerate in the opposite direction of their initial motion, thus a lot more energy would be needed to reach design velocity. That makes it necessary to carry a lot more fuel for the propellant and thus, the rocket can carry less explosives. For some moment the rocket would also have zero velocity.
On the analogy with the car: The exhaust gases do not carry enough momentum to actually have a nonneglibile effect.
The rockets would need to accelerate in the opposite direction of their initial motion, thus a lot more energy would be needed to reach design velocity. That makes it necessary to carry a lot more fuel for the propellant and thus, the rocket can carry less explosives. For some moment the rocket would also have zero velocity.
On the analogy with the car: The exhaust gases do not carry enough momentum to actually have a nonneglibile effect.