I am confused, here is a question:

A large truck and a mini bus both have same velocity V and they collide and stop. The collision lasts for 1 second.

A) Which one of the two will experience larger force of impact?

I am confused about the answer which is coming that truck will experience larger force. But Newton's Third Law of motion says that 'to every action there is an equal and opposite reaction'. So the force experienced by the truck should be same to that experienced by the car, but negative, isn't it?

Please help.

  • $\begingroup$ If a rifle bullet hits you, the bullet experiences exactly the same force of impact as your flesh. The consequences aren't equal due to the differences in the material, differences in weight and shape of the impact, but the impact force that slows down the bullet is exactly equal to the impact force that's creating a wound. Car collisions work in the same way. $\endgroup$
    – Peteris
    Commented Sep 21, 2014 at 9:25
  • 1
    $\begingroup$ Could it be "exert larger force" instead of "experience larger force'? $\endgroup$
    – bobie
    Commented Sep 21, 2014 at 10:42
  • $\begingroup$ No, the question was experience larger force. $\endgroup$
    – Saira
    Commented Sep 22, 2014 at 10:29
  • $\begingroup$ @abc : It makes no difference if the force is "exerted" or "experienced" - they are still the same. The force which one vehicle exerts is the force which the other vehicle experiences. $\endgroup$ Commented Jul 27, 2016 at 14:53

3 Answers 3


They both experience the same force because of the impact, due to the Newton's third law, like you say.

I think the question is not clear enough. If you assume there is no friction between the trucks and the ground, then you can use momentum considerations.

I know this shouldn't be an answer, but I'm new and I can't post a comment, yet.


The author of the question presumably expects you to notice these facts

  • both have the same velocity
  • they collide and stop
  • The collision last for one second

and to work out the total force acting on each vehicle from the change in their momentum.

The answer given is arguable correct if the author is talking about the total force (i.e. not just the force between them), but the question is faulty because your interpretation is at least as natural.


The question has illogical parameters that are probably not correct. It is unclear to what force exactly they are referring here.

Consider the following question: A mosquito and a truck collide; both have the same velocity; they collide and and it takes one second for them to stop.

That clearly illustrates the foolishness of the question. It sets parameters that are clearly not correct.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.