Newtons 3rd law with a truck hitting a person

[Painguy]

I having a little trouble grasping the 3rd law because of this idea in my head about a situation where a large truck going very very fast hits a person standing still.

1)Lets say the truck is going fast enough where the person's body will slightly rupture due to the impact. How can that tiny person exert such a large force back to the truck?

2)If during the collision the two bodies exert an equal magnitude of force on each other how is it that one of the bodies doesn't stop?

3)If the truck hit the person and continued moving in the same direction without hesitation then would the person start moving with the same force of the truck since its initial force was 0N or would it go flying ahead?

My guess for the last question is that person would move with the truck(if not on it). I figured that the scenario where the person goes flying is an exaggeration and that the person would seem to go flying ahead if the truck stopped after the collision. Thanks in advance. Sorry for all the questions I'm just genuinely curious. This isn't really a homework related question.

 

[Dick]

I having a little trouble grasping the 3rd law because of this idea in my head about a situation where a large truck going very very fast hits a person standing still.

1)Lets say the truck is going fast enough where the person's body will slightly rupture due to the impact. How can that tiny person exert such a large force back to the truck?

2)If during the collision the two bodies exert an equal magnitude of force on each other how is it that one of the bodies doesn't stop?

3)If the truck hit the person and continued moving in the same direction without hesitation then would the person start moving with the same force of the truck since its initial force was 0N or would it go flying ahead?

My guess for the last question is that person would move with the truck(if not on it). I figured that the scenario where the person goes flying is an exaggeration and that the person would seem to go flying ahead if the truck stopped after the collision. Thanks in advance. Sorry for all the questions I'm just genuinely curious. This isn't really a homework related question.

The truck exerts the same force on the person as the person exerts on the truck. Just face it. Using F=ma, then if the truck is much more massive than the person then the effect on the truck is much less than the effect on the unfortunate person. That's really the answer to all your questions.

 

[Painguy]

I appreciate the feedback, and I suppose your post answers my 1st question, but isn't there a more technical answer involving momentum and some other things for the other 3?

 

[Dick]

I appreciate the feedback, and I suppose your post answers my 1st question, but isn't there a more technical answer involving momentum and some other things for the other 3?

Sure there's a technical answer. Suppose the mass of the truck is M, mass of the person is m and initial velocity of the truck is v. On one extreme the collision could be completely inelastic where the person splats onto the front of the truck and sticks there. You can easily work out the final velocity of the truck using conservation of momentum and get Mv/(M+m), so if m is small compared with M the truck will continue with slightly smaller velocity. On the other extreme the collision could be completely elastic (the bouncy kind). Then you can use conservation of momentum and energy to find the final velocity of the truck is v(M-m)/(M+m) and the final velocity of the person is 2vM/(M+m). So again the truck has slightly diminished velocity but the person get bounced ahead at almost twice the speed the truck was moving. Make up some numbers and put them in and see.

 

[Nickie]

1) Newton's third law states that for every action, there is an equal and opposite reaction. In this scenario, the truck hitting the person is the action and the person's body rupturing is the reaction. The person's body is exerting a force back on the truck, but the truck is much larger and has a greater mass, so it is able to withstand the force and continue moving forward. This is similar to how a small ball hitting a wall will bounce back, but the wall does not move.

2) In this scenario, both the truck and the person are exerting an equal force on each other, but the truck has a greater mass and therefore a greater inertia. This means that the truck will continue moving forward while the person's body will absorb the impact and potentially be pushed back or thrown.

3) If the truck were to hit the person and continue moving in the same direction without hesitation, the person would move with the truck, either on it or being pushed by it. This is because the initial force applied by the truck on the person would cause the person to move with the truck, rather than flying ahead. If the truck were to stop after the collision, the person would still have the same initial force applied to them, but the force of friction between the person's body and the truck would eventually slow them down. This is why it may seem like the person is flying ahead if the truck were to stop suddenly.

It's important to remember that Newton's third law applies to the forces between two objects, not their individual motions. In this scenario, the truck and the person are exerting equal and opposite forces on each other, but their individual motions depend on their masses, inertia, and other factors. I hope this helps to clarify Newton's third law in this scenario.