Newton's Third Law Question

Question

Hypothetically, consider a scenario in which a man was exerting X amount of Newtons on a truck that is sitting in neutral on a hill, causing it to remain almost at rest. However, in seconds, the truck begins to slide down the hill. In this example, did the truck exert more, less, or equal to the X amount of newtons exerted by the man?

I thought that although the man's applied force on the truck of X newtons causes the truck to return X newtons, ultimately, the truck's applied force on the man due to gravity must be greater than his X force in net, as the truck is accelerating downwards. Am I right in this reasoning?

Answer 1

In your example, it is the difference between the component of the truck's weight down the slope and the force from the man pushing on the truck which results in the dynamics (the truck rolling downslope). So, in answer to your first question, the truck is exerting a greater force than the man if we presume the truck begins to roll downslope.

The reaction force of the truck on the man does not contribute to the dynamics of the truck; it affects the dynamics of the man (this is the force that simply pushes the man downslope as the truck rolls down the hill), presuming of course that the push exerted by the man remains constant.