A strong man from the circus is being driven in a car which is moving at a constant speed of 5km/h. He decides he will test his strength by trying to stop the car so he pushes on the seat as hard as he can in the direction opposite to the motion of the car. Why is he not able to stop the car?
The strong man is not able to stop the car because of Newton's first law of motion, also known as the law of inertia. This law states that an object at rest will stay at rest, and an object in motion will continue moving at a constant velocity unless acted upon by an external force.
In this case, the car is already in motion, moving at a constant speed of 5 km/h. The strong man pushing on the seat will indeed exert a force in the opposite direction, trying to slow down or stop the car. However, because of his location inside the car, the force he applies is internal to the system of the car, and his actions do not affect the overall motion of the car.
To stop the car, an external force would be needed, such as applying the brakes or using another external force like friction or air resistance. The strong man's force, being internal, does not have any impact on the car's motion.
The strong man is not able to stop the car because the force he exerts on the seat is an internal force, meaning it is acting on a different object within the system. In this case, the force he applies on the seat is acting on the car itself. According to Newton's third law of motion, for every action, there is an equal and opposite reaction. Therefore, the force being applied on the car is being countered by an equal and opposite reaction force from the car.
Since these internal forces cancel each other out, they do not have any effect on the car's overall motion. The car will continue to move forward at a constant speed of 5 km/h, unaffected by the strong man's attempt to stop it. In order to stop the car, an external force would be required, such as applying the brakes or creating friction with the ground through another means.