Final answer:
The cart and the hand are interacting during the contact phase of a push, where the hand applies a force to the cart causing it to accelerate. This is known as impulse and it results in a change in momentum of the cart.
Step-by-step explanation:
In the context of a push, the cart and the hand are interacting during the contact phase. This is when the hand applies a force to the cart, causing it to accelerate. The force exerted by the hand creates an equal and opposite reaction force on the hand from the cart, according to Newton's third law of motion.
During this interaction, the cart and the hand experience an impulse, which is the product of the force applied and the time interval over which it is applied. The impulse causes a change in momentum of the cart, resulting in its acceleration.