Final answer:
The force exerted by the shopping cart on the shopper is 50 N in the opposite direction, in accordance with Newton's third law of motion. The forces are equal in magnitude and occur as a pair acting on different objects.
Step-by-step explanation:
If a 50 N force is exerted by a shopper on a shopping cart to push it forward, according to Newton's third law of motion, which states that for every action, there is an equal and opposite reaction, the shopping cart exerts an equal force of 50 N on the shopper but in the opposite direction.
It is important to understand that while the forces are equal in magnitude and opposite in direction, they act on different objects, which is why both the shopper and the cart can still move in the direction of the applied force.
The scenario given in the question is a classic example of Newton's third law at work. When the shopper applies a force to the cart, the cart applies a reaction force back onto the shopper.
However, since the shopper car is usually heavier and the cart has wheels, the resistance is primarily due to friction, and thus the shopper doesn't move backward significantly. Instead, the cart accelerates forward if the resulting force overcomes friction.